I have an Audi a4 with halogen lighting, I will be converting to xenon pretty soon and I'm putting together my own harness to drain power straight from the battery and not from the bulb plug. Now, my car sets off an warning if a bulb is out (not plugged in), the car uses H7 55watt Halogen bulbs, can a resistor solve my problem? Thanks in advance.
Re: Is there a resistor I can put in my bulb socket to emulate a current draw?
December 1 2003, 11:37 PM
most definitely. The easiest thing to do is measure resistance across the two terminals on one of your H7 bulbs. Now just hunt down a resistor of that value. It should be roughly about 4 ohms. Plus or minus 10% and the car shouldn't give you any fuss.
Re: Re: Is there a resistor I can put in my bulb socket to emulate a current draw?
December 2 2003, 2:59 AM
But that will make a lot of heat, AND it defeats the power savings of have xenon in the first place. You just need to hunt down the wire (from a schematic) that ties the headlight wires (R & L respectively) to the message center, then disconnect them from the headlight circuit, and THEN put your resistor into that circuit so it doesn't have 12v running through it. Or if your car ever came from factory with xenon as an option, some of these newer cars like this can be reprogrammed at the dealer in the PCM to 'see' the xenon resistances. But your car had to come with xenon as a potential option for that to even be a possibility, and it obviously still may not even work if you had relay harness. I would just clip the sense wires if it was me and then give them the right resistances like I said before. To me that is easiest and wont draw any more power nor create any heat
Ok, so going with what you told me, theoretically, a 4ohm resistor should do the trick, once I check I'll know for sure, but besides the ohms, what resistor should I get?? Assuming it's a 12 volt 55 watt plug, do I have to get a resistor that handles 12 volts and/or 55 watts as well? Thanks.
Al,
Josch brought up some really good points. I'm sure Herman's link has plenty of good info as well.
I double checked my math, and came up with 3 ohms instead of 4, but I'd probably just use a multimeter to be certain. If you wanted to put a resistor in your bulb socket, then yes, you'd need one that would handle over 55 watts.
Hey Josch, explain your method to me a little better. I grasp the concept, but don't completely understand.
They do indeed bring up good points, the waste of energy and heat are a burden but looking up the schematic on my wiring to find this bulb out sensor poses a bigger issue for me. Also I found out that option of halogen or xenon is wired down to the specific ecu of the car and is not programmable, I may be wrong about that, but that's what I heard. I'll be trying the resistor method to see how that goes. Thanks to everyone for their insight and recommendations.
what i dont understand is how ur going to turn them on? u want to use ur oem switch right? if u trigger ur relays off the oem wiring then u should have no light go on in ur dash.
Ok, I thought about that, I'm going to run a harness that has a relay built in that detects power from the oem plug, that's fine, the only thing is that the harness plugs into only one of the two H7 plugs, leaving the other one unplugged. Can I run power from the second oem plug to the relay as well? I'd rather do that then to put in a resistor that's only going to drain power and create unnecessary heat. Any thoughts?
Alfonso,
You could just plug a factory halogen bulb into the unused side of the original harness; that would fool the computer (on that side at least). You'd also be sucking 55W of power from the system for no good reason. The easiest thing to do is locate the bulb out signal wire to the message center, cut the wire in two, and tape both ends off.
