# Wiring it up - My First Megasquirt System



## 16ValveInside (Nov 20, 2004)

I got my MS ecu so its time to get started with my first megasquirt install. I'll have a lot of questions along the way and your feedback is welcome. Since all these wires except maybe 2 are going to the engine compartment anyway, I decided to put the ecu in the rain tray instead of running all those wires from the inside of the car to the engine. There was a already a threaded stud and a post there from the original Digi II ecu bracket mounting, I enlarged the hole in the MS ecu flange for the stud, and then popped a rubber grommet over the post that the original ecu bracket used, and filed that corner of the MS ecu flange down just enough to slide it into the slot in the grommet. I just hate drilling holes when I don't have to. I going to fabricate a small triangular bracket to connect the 2 holes on the other end of the MS ecu to the post that secured the rear of the orginal DigiI I bracket. 



















Now I'm trying to figure out if I can tap into the wires in this connector that went to the original module, instead of going to the fuse box for fuel pump trigger and power. This is a 91 GTI Digi II car. 










So far I've determined that: 

Red/White - Heated Oxygen sensor + 12v supply 
Red/Yellow - Fuel Pump Relay signal to ECU 
Red/Green - Starter cranking signal 
Black/Yellow - +12v from digifant relay 
Red/Black - ? Main Fusebox Starter Power? (goes to coil) 
White/Red - ? maybe for MFA option 

Could I just use red/yellow for fuel pump trigger and black/yellow for power ?


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## ps2375 (Aug 13, 2003)

Is your MS box water-proof? if not, the raintray is not a good choice for mounting it. And you still have to run the tuning cable thru the firewall, why not just mount the MS inside the car and only have to deal with the firewall pass-thru on install and not every time you do some tuning?


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## ps2375 (Aug 13, 2003)

I just use stock relay to control FP, or wire in switched power to a relay and have the MS control FP. What are you using for a wideband?


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## 16ValveInside (Nov 20, 2004)

ps2375 said:


> Is your MS box water-proof? if not, the raintray is not a good choice for mounting it. And you still have to run the tuning cable thru the firewall, why not just mount the MS inside the car and only have to deal with the firewall pass-thru on install and not every time you do some tuning?


 no its not waterproof, but my rain tray cover is good and I don't have clogged up drains. Was the original Digi II ecu waterproof? This will not be a daily driver, more of a weekend street car. And as far as the tuning cable, why can't I just open the hood, plug in the tuning cable, and then pass it through the window to a laptop.


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## ps2375 (Aug 13, 2003)

Yes, the original ECU is waterproof. If you want to risk it, then go ahead. And if you have a cable that long, have fun with that.


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## 16ValveInside (Nov 20, 2004)

So far I've determined that: 

Red/White - Heated Oxygen sensor + 12v supply 
Red/Yellow - Fuel Pump Relay signal to ECU 
Red/Green - Starter cranking signal 
Black/Yellow - +12v from digifant relay 
Red/Black - ? Main Fusebox Starter Power? (goes to coil) 
White/Red - ? maybe for MFA option 

In the Bentley it shows that red/yellow wire connects to fuel pump relay termimal 85, which is exactly where my purple MS- terminal 37 wire needs to go. So is there any reason that I can't just 
connect to the red yellow wire in the picture above? 

Also the Bentley shows that black/yellow wire connects to Digi control unit relay terminal 87, which is exactly where my red MS 12V+ switched- terminal 28 wire needs to go. So I should be able to connect to the black yellow wire in the picture above for MS power after adding a 2 amp in line fuse, correct?


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## L33t A2 (Aug 5, 2003)

*FV-QR*

Mount that crap to the passenger side of the center console, route the wires behind that and the kneebar/under dash tray and out of the grommet directly to the left of the steering column...


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## 16ValveInside (Nov 20, 2004)

L33t A2 said:


> Mount that crap to the passenger side of the center console, route the wires behind that and the kneebar/under dash tray and out of the grommet directly to the left of the steering column...


OK, tough crowd, I'm moving the ecu inside the car, and yes I had already been eyeing up those 2 grommets/holes to the left of the steering column as a good place to route the wires, if I was going to put it inside. So making progress I'll have some pics posted soon.


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## bonesaw (Aug 8, 2004)

Or check to see if grommet by AC holes and put in glove box


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## 16ValveInside (Nov 20, 2004)

I pulled the firewall plug out that was to the left of the steering column, and I have a assortment of grommets so I grabbed the one that was the closest to the size I needed and I really lucked out, it fit perfect. I did not measure it, just stuck it in. Not only that but the ID is the perfect size for the split loom to slide through, just barely enough room and man it is tight.



















I think I'll just mount the control unit on top of the tunnel under the dash with the front of it just flush with the front of the flat euro console cover. That way I'll have easy access to plug the tuning cable right in.


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## fakename (Apr 5, 2012)

Any worry about it being directly under your heater core if you mount it there? I've got mine wire tied around my non-AC heater between the blower and the center console. Even without my knee bar, it can't be seen (keep lookey-loos from noticing that this thing isn't stock and therefore more fun to steal, although boost controller is kind of a give away...). But back on point, if your heater core goes in a bad way, might leak hot coolant all over your MS...


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## 16ValveInside (Nov 20, 2004)

fakename said:


> Any worry about it being directly under your heater core if you mount it there? I've got mine wire tied around my non-AC heater between the blower and the center console. Even without my knee bar, it can't be seen (keep lookey-loos from noticing that this thing isn't stock and therefore more fun to steal, although boost controller is kind of a give away...). But back on point, if your heater core goes in a bad way, might leak hot coolant all over your MS...


Good info, I 've got a non ac box as well, but my heater core is new and this is not a daily driver. 
So I'm not too much worried about it.


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## 16ValveInside (Nov 20, 2004)

sure takes time to get everything you need, to even begin making your own wiring harnes.
I mean we are dealing with 20 gauge TXL wire and you have to have connectors for that 
gauge/range of wire, not to mention:

*heat shrink*
*heat gun* for the heat shrink
*wire covering*, I like the split loom, of course you need at least 3 different sizes and make sure you get the high heat nylon not the cheap polyethylene stuff
*connectors*, metal crimp style for 20 gauge wire, male, female, end to end
*crimper*, wide range for both crimps on the metal connectors 
*fuses*, 2 amp for switched power, 5 amp for fuel injectors
*fuse block panel* or in line fuse holders with connectors for 20 gauge. 

its almost like a chess game, before you make one move, cut or crimp one wire, you have to look ahead several move to see what the results will be within the big picture of the harness


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## ewillard (Apr 21, 2007)

How have u made out I'm curently rewiring mine. To clean it up and add a few things 

Sent from my ADR6425LVW using Tapatalk 2


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## Bandwidth (Jul 8, 2009)

What throttle body are you using? I'm thinking of using the stock to avoid the issue with getting a tps TB. Thoughts from people who have gone this route? I just finished assembling my MS just waiting for my spare VW harness go get here so I can use it for the connectors


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## 16ValveInside (Nov 20, 2004)

Bandwidth said:


> What throttle body are you using? I'm thinking of using the stock to avoid the issue with getting a tps TB. Thoughts from people who have gone this route? I just finished assembling my MS just waiting for my spare VW harness go get here so I can use it for the connectors


 passat auto t/body with TPS, but I wish there was a less expensive alternative to something else. 
But I like the idea of using a TPS , even though MS will perform without one


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## 16ValveInside (Nov 20, 2004)

ok so I've got wires in the engine compartment and getting good at crimping, just a matter of getting the right crimper

[


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## 16ValveInside (Nov 20, 2004)

decided to make a separate sub harness for the fuel injectors using a 6 pin weatherpack connector, just in case I ever
have to pull the engine, should make it easier.

[


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## 16ValveInside (Nov 20, 2004)

then started wiring up the injector harness













I,m going to mount the connector to one of the intake manifold brackets at the back


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## bomberbob (Sep 19, 2004)

Hey, you do good work. I work at a place that builds harnesses for cranes and stuff. Heat shrink over your split loom, weatherpack connectors, good stuff. I should have went that route.


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## sdezego (Apr 23, 2004)

Very meticulous. Did you ever get your question sorted out to that 6 pin plug in the rain tray or is it no longer relevant since you moved the ECU in the cabin?

G60 Digi used 2 separate plugs similar that yours and you can tie everything in via it/them. w/o looking I am not sure but the other wire may be for ISV power.


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## 16ValveInside (Nov 20, 2004)

sdezego said:


> Very meticulous. Did you ever get your question sorted out to that 6 pin plug in the rain tray or is it no longer relevant since you moved the ECU in the cabin?
> 
> G60 Digi used 2 separate plugs similar that yours and you can tie everything in via it/them. w/o looking I am not sure but the other wire may be for ISV power.


yes I did, I tapped into those existing wires that I needed instead of messing with going into the fuse box. Thats where they come from anyway, much cleaner.

I used red/yellow for fuel pump trigger and black/yellow for switched power.


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## sdezego (Apr 23, 2004)

:thumbup:


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## ValveCoverGasket (Mar 20, 2002)

sdezego said:


> Very meticulous.


indeed! looking really good :thumbup:


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## noddaz (Aug 5, 2004)

*current status..?*

running yet? I find this fascinating.... Because I need to do this sort of work on my 86 GTi...


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## 16ValveInside (Nov 20, 2004)

I am wiring up my tps sensor, which is just ground, tps sig, and 5v ref, simple enough, but wiring up the hall I just jump off the 5v ref also for hall power, and a ground, but I could not find the hall signal wire which should be pin 24 wire. Well, I finally found it. I pulled the DB37 connector apart to get a look at the wires and found it, pin 24 has a solid light gray wire connected to it and pin 24, pin 1, and pin 2, are all together in one of those wires that look those SPR/extra wires that I just left in the car rolled up. Its a has a white case with braided inner liner and the markings on the wire cover are,

WHITE: Crank CKP +/RPM input Black: ckp-E17 1197 22 awg 2c (UL) cmp c (UL) US 150 C FT6 ROHS, but no DIY autotune or Pin 24 ID on it.

I ran the wire out in the engine compartment, but should I just put a connector on the pin 24 gray wire, are just put all 3 in one connector?


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## bonesaw (Aug 8, 2004)

its a sheilded wire. you will use the two wires and also connect 5v. look at the megasquirt diagram.


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## carsluTT (Dec 31, 2004)

looking clean. keep at it


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## the dubshow (Mar 18, 2008)

nice clean work. Im about at the same point on my rabbit efi setup. 

Which crimp tool did you end up buying? The $100 one from diy? I went cheap and it was a was of $30...


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## 16ValveInside (Nov 20, 2004)

the dubshow said:


> nice clean work. Im about at the same point on my rabbit efi setup.
> 
> Which crimp tool did you end up buying? The $100 one from diy? I went cheap and it was a was of $30...


I've been buying most of my connectors, terminals, etc from Ballenger Motorsports and the 2 crimpers that I use the most, and that work well, are
Part# TOOL-01000 and # TOOL-01001

http://www.bmotorsports.com/shop/index.php/cPath/111_112_170


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## 16ValveInside (Nov 20, 2004)

*Wiring up the 14point7 Spartan Wideband Lambda Sensor:*

First of all a switched power source. I need a power source thats live only when engine is running, vs. one that has power when the engine is spinning over prior to starting.

Don't the main & fuel pump relays supply power while starting also? All the wiring diagrams I've seen show wideband switched power source at main or fuel pump relay terminal # 87.


And on the 5 sensor wires : correct me if I'm wrong

Red - switched 12V power when engine is running, not when spinning over before starting
Black - ground at ECU, pin 1 or 2
White - gound at engine block
green - to ECU pin 23, O2 sig
brown - not used


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## ps2375 (Aug 13, 2003)

I have my JAW unit powered from a 12v switched relay. Not the same as my pump which is controlled by MS. I have 3 relays, one for the FP, one for MS & WB and KS and the last for coil, IAC and injector power. (W/O looking, I think that is how I have them powered and then fuses for each.)





As for wiring the Spartan, it should have instructions that came with or when his site get back up, the info is available there.


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## bonesaw (Aug 8, 2004)

i would wire WB so that it is only on when car is running. Maybe off fuel pump relay circuit.


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## 16ValveInside (Nov 20, 2004)

bonesaw said:


> i would wire WB so that it is only on when car is running. Maybe off fuel pump relay circuit.


yes, looks like terminal 87 off of fuel pump relay is the place to go :beer:


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## 16ValveInside (Nov 20, 2004)

16ValveInside said:


> yes, looks like terminal 87 off of fuel pump relay is the place to go :beer:


actually, even better, the Red/White wire in that connector in the rain tray ( 3rd pic from top of this thread) from the fuse box is for - Heated Oxygen sensor + 12v supply

I'll just run a wire w/correct terminal in the other side of the connector and plug right in. Its times like this that I'm glad I'm converting a 91 8V GTI Digi 2
car, to a 16V w/megasquirt, instead of going from a original 91 GTI 16V w/Motronic, to megasquirt.


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## need_a_VR6 (May 19, 1999)

I have always used key switched power so I can have it heated during a cold start if I want to log.


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## ewillard (Apr 21, 2007)

the corrado has similar wires but its split into 2 plugs . but i could never get MS to control my FP. i had to wire my FP to just comes on as soon as i have the key turned on. ill have to look again how i have it wired. any help on how it should be. 


Three pin connector:
1. R/W goes to the O2 sensor connector. 
2. R/Y (smaller one) goes to ECU pin 3, fuel pump relay
3. R/Y (larger one) goes to fuel injector harness

Four pin connector:
1. R/G goes to ECU pin 1 (start)
2. BK/Y goes to ISV and ECU pin 14. (Splits inside the harness)
3. Y goes to ECU pin 20 (check engine light) 
4. BK/W goes to ECU pin 23 (ECU relay)


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## sdezego (Apr 23, 2004)

ewillard said:


> the corrado has similar wires but its split into 2 plugs . but i could never get MS to control my FP. i had to wire my FP to just comes on as soon as i have the key turned on. ill have to look again how i have it wired. any help on how it should be.
> 
> 
> Three pin connector:
> ...


Yes I tapped everything into those plugs and just cleaned up some wiring recently. I'll see If I can find my wiring, but definitely trigger my FP directly from one of those connectors. I seem to recall my wire colors being a bit off from the Bentley though.

I do trigger my LM1 wideband via a key switched relay though and didn't run via those connectors (not that you couldn't or shouldn't)

S


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## sdezego (Apr 23, 2004)

Yep, wired purple from MS to Middle pin (#2) of that 3 pin connector. Beware as some descriptions show #3 as Fuel Pump Output. This is actually off of the FP relay (i.e. + power from #87 contact to power injectors)

Also powered MS via T3B2 (pin 2 of 4 pin connector)

Remember that MS will only trigger FP for a sec when you turn on key (enable in TS) and then again when it senses a Crank or Run condition.


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## ewillard (Apr 21, 2007)

the problem i had was when i had it wired "correctly" i could not get power to the ecu even. ill look at my wiring today and see what up. i dont have my motor back fro machine shop yet so i have plenty of time to deal with wireing


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## need_a_VR6 (May 19, 1999)

Obd1 cars are a bit goofy with the 109 relay. All you need to do is not use it and things get simple.


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## ewillard (Apr 21, 2007)

That's the ecu relay correct? Should it be changed to something diffrent or not use all together 

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## need_a_VR6 (May 19, 1999)

Yes. I wire it so its not usd at all.


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## sdezego (Apr 23, 2004)

ewillard said:


> the problem i had was when i had it wired "correctly" i could not get power to the ecu even. ill look at my wiring today and see what up. i dont have my motor back fro machine shop yet so i have plenty of time to deal with wireing


 Pin#2 of 4 wire plug for MS power (bk/y)


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## ewillard (Apr 21, 2007)

ewillard said:


> Three pin connector:
> 1. R/W goes to the O2 sensor connector.
> 2. R/Y (smaller one) goes to ECU pin 3, fuel pump relay
> 3. R/Y (larger one) goes to fuel injector harness
> ...


Here's how I had to wire mine to get it to work. 

3 pin connector 
1) thick red/yellow to inj pos
2)small red/yellow to ground
3)red/white to awic water pump

4 pin connector
1)black/white to red/white on 3 pin connector 
2) yellow no where
3)black/yellow to ecu power
4)red/green no where 

This is the only combination that would work. I'm going the wire it how it should be and see how things go. But we will see. 


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## 16ValveInside (Nov 20, 2004)

Wires everywhere but making progress.
Wiring up my Spartan Wideband to make it easier to replace, IF, it ever goes bad. On the power wire used a male / female connector with heat shrink over the connector and on
ground & signal wires heading back to the ECU used a 2 pin weatherpack connector.

spartan wiring where it splits off for power, 2 for the ecu, and ground to engine block



and connector heading to ecu


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## MEGA 16v GLI (Aug 31, 2010)

Any idea what you are going to do with that fuel tank vapor hose that connects to the big black rubber intake boot (just above the air box)?


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## the dubshow (Mar 18, 2008)

any updates?! I finally got my MS to talk to my computer off of stim... Never again rs-323...


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## 16ValveInside (Nov 20, 2004)

No real updates, I just moved from Texas to South Carolina. I had the car shipped on a car transport and its waiting in the garage.
I will get back to work on it next weekend.


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## leebro61 (Nov 7, 2001)

16ValveInside said:


> No real updates, I just moved from Texas to South Carolina.


What part of SC?


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## 16ValveInside (Nov 20, 2004)

So, still working on this when I have some free time that is. I have my catch can finally installed and my vacuum log/manifold installed. 
Will update soon, as I am sure after I get Tuner Studio loaded on my laptop and I'm getting ready to fire it up I will have some questions.


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## 16ValveInside (Nov 20, 2004)

Well the engine starts and really sounds good but will not idle, so I've been doing some checks.

Just checked for power with key in the on position at ecu and getting power from the first 6 pins on the bottom row if counting from the left which I think are pin #'s 20 through 25 and also the 10th pin which I think is # 29

Which is odd because my wiring diagram shows pin #6 and #10 as auxillary wires.

Also that would indicate that the TPS sensor #7 and main relay #9 don't get power with the key in the on position.

But I'm trying to figure out how these wires have power with just having the key in the on position


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## need_a_VR6 (May 19, 1999)

Those pin # sound odd as 1-2 and 7-19 are all grounds in a normal ms harness.


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## 16ValveInside (Nov 20, 2004)

Thanks Paul,



need_a_VR6 said:


> Those pin # sound odd as 1-2 and 7-19 are all grounds in a normal ms harness.[/QUOTE
> 
> Yes with connector/harness unpluged from the ecu and looking at the connector I'm checking at the connector pins that connect to the ecu and thes are on the botttom row counting left to right.
> 
> ...


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## 16ValveInside (Nov 20, 2004)

need_a_VR6 said:


> Those pin # sound odd as 1-2 and 7-19 are all grounds in a normal ms harness.


Thanks Paul,



need_a_VR6 said:


> Those pin # sound odd as 1-2 and 7-19 are all grounds in a normal ms harness.[/QUOTE
> 
> Yes with connector/harness unpluged from the ecu and looking at the connector I'm checking at the connector pins that connect to the ecu and thes are on the botttom row counting left to right.
> 
> ...


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## need_a_VR6 (May 19, 1999)

Wire colors are right make sure you are checking the right pins. Most diagrams are shown looking at the connector back toward ecu, so if you are looking at the harness connector unplugged it would be the reverse.


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## 16ValveInside (Nov 20, 2004)

Well then that would mean that the fuel injectors, the fuel pump relay, and maini relay are getting power with the key in the on position


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## need_a_VR6 (May 19, 1999)

That makes sense if measuring the ms side. 12v would mean the output is off, ground would be on.


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## Jettaboy1884 (Jan 20, 2004)

That was a big gap in time there for a while. Just curious what the current state of things is with the car?

I'm currently (barely) running bike carbs on my 8v but am thinking of making the plunge into MS for long-term purposes. I'm eager to hear how it has worked out for you. :thumbup:


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## 16ValveInside (Nov 20, 2004)

Well, sometimes its the little things that make such a_ *big* _difference.

I finally got the engine to idle. It would always start and I could keep my foot on the gas and it and rev it up and and it would sound great, but anything less than about 2500 RPMs it would just turn off.

I was talking to a friend of mine who has a _great _amount of automotive experience, and we were reviewing things like wiring diagrams, settings and he questioned where did I mount my MAP sensor.

I told him it was inside the Megasquirt ECU and I have a vacuum hose from the ECU to the throttle body. 

And he quickly said well that couild very well be your problem, because you need manifold vacuum not port.

And I was thinking could be really be that easy???? So I removed the vacuum line from the the throttle body, put a vacuum cap on it and attached the vacuum line to the back of the intake and statrted it up.

As soon as it started I revved it up to about 2500 and then let off, and it was idling at 1000 rpms in a smooth awesome sounding idle, and all I did was reposition the vacuum hose for the MAP Sensor.

Amazing, this is a project car, a 1991 16v GTI and I started this project in 2004. I bought this car in 2004, drove it home and parkied it in the middle of the garage and took it completely apart and have been working on it in my spare time since.

Complete trans and engine disassembly and reassembly with goodies, and the list goes on and on about what I have done to this car and now I can finally drive it!!!!!!

I am also going to use a T vacuum fitting at that location and attach the vacuum hose from the fuel pressure regulator to the same vacuum source at the back of the 16V manifold.

Amazing. All that time questioning myself and going over wiring diagrams in my head and retracing my steps only to find I need to move a vacuum line from the throttle body to the intake manifold

Many thanks to _*Spitfire EFI*_ and Paul at_* KPTuned!!*_


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## need_a_VR6 (May 19, 1999)

Wow, I have had that happen a handful of times over the years and it is not an easy find. Especially if you think the tb port is on the manifold side! Usually happens with the booster check valves as those see manifold vac but not a great source. 

Glad you found the glitch and its smooth sailing!


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## ValveCoverGasket (Mar 20, 2002)

That's awesome news!
I've definitely been fooled by those closely place small bore vacuum nipples on the VW throttle bodies... They mount at an angle and you can't quite tell which is pre and which is post TB

Now the fun part - getting it dialed in!


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## banjopete (Apr 28, 2013)

Thanks for all the details and info. I'll be hanging onto this link for the future. 15 years on the car project gives me hope too.

Sent from my SM-T820 using Tapatalk


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## sdezego (Apr 23, 2004)

You have no idea how many G60 owners mixed up the 2 ports on the back of the TB...


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## need_a_VR6 (May 19, 1999)

sdezego said:


> You have no idea how many G60 owners mixed up the 2 ports on the back of the TB...


Literally all of them at least once.


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