# 1991 cabriolet oil pressure question



## sdavidson7014 (Feb 20, 2008)

Hi guys my name is spencer im new to the Cabriolet world, before this MK1 i had a MK4 gti. Im restoring this Cabby to be my daily, for the most part things have been going good but the first question ive come across is this oil pressure sender/switch on the side of the head. I read on cabby-info.com when the yellow wire running to the switch is grounded the light will flash. so my question is, should this wire not be grounded? or does cabbyinfo mean it will on light when the wrong pressure is detected and the wire is grounded. My light was flahing on the dash only at idle, i replaced the other pressure switch on the OF housing and now it seems to flash even when accelerating. When i pull this wire from the ground the light doesnt flash. The wiring was done by the previous owner so im not sure how correct it is. Pic of sensor and wire in question








*And the car just to be a whore*:heart:








Any info or help is appreciated!:thumbup:


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## sdavidson7014 (Feb 20, 2008)

Up.


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## erty67 (Feb 23, 2010)

Wish I knew more to help, but all I can add is that looks more like a oil pressure gauge sending unit than the stock switch. Do you have an oil pressure gauge?


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## Glegor (Mar 31, 2008)

erty67 said:


> Wish I knew more to help, but all I can add is that looks more like a oil pressure gauge sending unit than the stock switch. Do you have an oil pressure gauge?


cabbys had an oil pressure gauge. the correct sender has 2 connections on it, one for the gauge, and one for the retard light..


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## sdavidson7014 (Feb 20, 2008)

Yes this have 2 connections on it. One for gauge one for light. My question is, is this wired up correctly because my light is constantly flashing (no buzzer) but the oil pressure seems to be fine and car drives with no problems. Thanks again


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## WaterWheels (Aug 14, 2005)

sdavidson7014 said:


> My question is, is this wired up correctly because my light is constantly flashing (no buzzer) but the oil pressure seems to be fine and car drives with no problems.


If it is wired up correctly can't be determined from the picture as you can not see the markings for the terminals. What exactly do you mean by ". . . but the oil pressure seems to be fine . . ."? Is the gauge also not working or do you mean the reading looks fine? May seem like a stupid question but the answer could be important.

By the book, that means the way the factory set it up, that yellow wire is connected to a low pressure switch installed in the cylinder head. In this case because a "dual" sender is installed as a gauge is also used (sender also has a switch inside and is why it has two connections). The switch at the cylinder head, low pressure, is a normally closed switch (NC). So as soon as the ignition is switched on power flows through it to ground and the oil warning light comes on (that is why your oil light always comes on when you start your car). As soon as the engine starts and oil pressure increases past the low pressure switch setting, most times around 4-5psi, the switch contacts inside are broken and the light goes off. That is why in repair manuals they tell you to ground that yellow wire while the engine is running to test the low pressure side, grounded = light on and not grounded = light off = low pressure part of warning system working (not the switch).

So, with that said, here is what you can do to maybe track down the problem. Remove the yellow wire, making sure it does not touch any metal and start the engine. Does the light still flash? If yes then you have to test the yellow wire for a dead short to ground. No short found? then the warning circuit in the instrument cluster is defective. When you started the engine with the yellow wire removed and the light stayed off, then the sending unit is defective. Could be a piece of gunk stuck in it (sometimes happens when installing them or doing an engine fluch) or just plain old bad, but it is staying closed and should be open with the engine running.


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## erty67 (Feb 23, 2010)

sorry, I tried helping. Sadly my rabbit only has a switch. I didn't realize the cab was different.


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## sdavidson7014 (Feb 20, 2008)

thank you guys for the help so far, when i start the car with the yellow wire unplugged and not grounded. the light stays off for good. So by this happening you think its the sending unit? if so where could i pick one of these up? thanks again in advance:thumbup:


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## Glegor (Mar 31, 2008)

sdavidson7014 said:


> thank you guys for the help so far, when i start the car with the yellow wire unplugged and not grounded. the light stays off for good. So by this happening you think its the sending unit? if so where could i pick one of these up? thanks again in advance:thumbup:


wire off switch/sender makes the light go out. ground it out, it should set off all the bells and whistles..

i recently had a ground problem in my rabbit, and it tried using the oil pressure switches as a source of ground i guess, because my oil light NEVER goes out now. i still have 30psi oil pressure @ hot idle.. but the light is always faintly lit. i think its from an injured oil pressure switch/sender..


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## WaterWheels (Aug 14, 2005)

sdavidson7014 said:


> . . . when i start the car with the yellow wire unplugged and not grounded. the light stays off for good. So by this happening you think its the sending unit? if so where could i pick one of these up?


Bad or stuck closed for one reason or another, really doesn't matter as it would be hard to fix if it can be fixed and it's also old so lets just call it bad (broken). You never stated if the pressure side was working correctly, as far as you can tell, or not? I know places in Europe to get the senders but can't help you over there. The cost will be around $60 for a good one with both the switch and gauge sender together in one sender. They come without the switch also for cheaper and with a "T" fitting you can still have both the gauge and factory warning system working that way if you want. I suggest getting the correct one to avoid a mess under the hood. You can also just leave the wire off and watch the gauge if it is working OK or just get a "T" fitting to install a factory low pressure switch and keep the sender you have if it is functioning for the gauge (cheap way really but again more clutter). So you see there are options and your funds and searching ability will help you decide how to go.

Check VDO if they have an English/American web site version as they should carry a few different versions. Be sure to get the correct one or the warning system will still cause problems. It gas to be the correct one for your gauge *and* have the correct pressure setting for the switch.


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## sdavidson7014 (Feb 20, 2008)

Thank you guys for your help. I ordered a new switch/sender unit and im currently waiting for it to come in. Just gonna see if this takes care of my problem, if not i will have to explore more options. By the way i said the pressure was fine because of the car driving pretty clsoe to perfect not sure about these cars but when my mk4 had a oil pressure problem i could defiantly tell a difference in the way it drove. I guess we will see, thanks again for the help:thumbup:


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## kamzcab86 (Feb 14, 2002)

http://cabby-info.com/gauges.htm#oil:
Test the low-pressure switch on the cylinder head by removing the yellow wire; if the warning light stops flashing, the switch is faulty and should be replaced. 

The proper sender/switch is sold by German Auto Parts and the like.



sdavidson7014 said:


> By the way i said the pressure was fine because of the car driving pretty clsoe to perfect not sure about these cars but when my mk4 had a oil pressure problem i could defiantly tell a difference in the way it drove.


Definitely NOT the thing to do. Always test the oil pressure with a proper mechanical oil pressure gauge; do NOT rely on the slightly inaccurate gauge in the car and do NOT rely on the car's "feel". 

Also, use the proper oil filter and oil weight: http://cabby-info.com/engine.htm#oil . You can also upgrade the oil pump to relieve minor oil pressure issues. :beer:


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