# Which resistor for Audi canbus?



## SteelCityMafia (Oct 18, 2012)

I have LEDs for every bulb in my car excluding the high beams. Everything is already installed and looks great, even have the resistors in the turn signals. But my car is a 2001.5 Audi a4 and it has the canbus brake light warning system. 

My question is: what resistor do I need for the third brake light? 

It normally has five 194 bulbs in it. It now has five 194 LEDs and is throwing a code on the dash.


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## dennisgli (May 17, 2003)

So according to donsbulbs a 194 is equivalent to 50ohms - so five would be 10ohms. 

So the question is what is the effective resistance of your LEDs?


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## SteelCityMafia (Oct 18, 2012)

dennisgli said:


> So according to donsbulbs a 194 is equivalent to 50ohms - so five would be 10ohms.
> 
> So the question is what is the effective resistance of your LEDs?


 I'm not sure. They are just eBay 194 5 led bulbs


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## dennisgli (May 17, 2003)

So you could measure the current that the LEDs draw. 

Or just guess! I'd just try something like 20ohms and see if that works. 

But thinking about this some more I don't actually know how these "bulb out" circuits work? Do they sense that the bulb is out when it is off? Or only when it should be lit? I was assuming the latter. The resistance when an incandescent bulb is off is much lower.


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## SteelCityMafia (Oct 18, 2012)

dennisgli said:


> So you could measure the current that the LEDs draw.
> 
> Or just guess! I'd just try something like 20ohms and see if that works.
> 
> But thinking about this some more I don't actually know how these "bulb out" circuits work? Do they sense that the bulb is out when it is off? Or only when it should be lit? I was assuming the latter. The resistance when an incandescent bulb is off is much lower.


 Well, it's trippy. As soon as you unplug the harness from the third brake light, the cluster beeps and shows brake light warning. So after I put the LEDs in, it just never shut back off. Now though, when I start the car, it stays off until the first time I hit the pedal, then stays lit. 

Well I bought the superbrightleds.com really good canbus resistor LEDs for the actual 7528/1157 bulbs in the taillights, and since I've installed those, if my parking lights are off, the warning just stays lit, probably because of the third brake light. But if I have the parking lights on, it stays lit and EVERY TIME I hit the brake pedal and they go to their second stage, it beeps again letting me know I have another light out. It's horrible. So after driving like this for like three months I'm getting tired of the beeps. So I'm going to put regular bulbs back in the tails and try finding the correct resistor for the third light, then once it's squared away find the appropriate resistor for the other two.


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## dennisgli (May 17, 2003)

Hold it - how do you know the problem is with the third brake light? Is there a separate "bulb out" warning for it? If you put the correct bulbs in for the left and right brake lights to you still get the warning? 

I'm not sure what a "CAN bus LED" is - neither the LEDs nor the resistors connect to the CAN bus. Have you asked superbrightleds.com about the problem? I suspect their "really good canbus resistor LEDs" may not be all that good!


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## SteelCityMafia (Oct 18, 2012)

I don't know that the problem is the third brake light. I know that the problem is all three, but I'm going to start with the third. Haha. And I've live chatted with them and they have no idea.


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