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Car Forum / Volvo Cars / June 2006headlight wiring question for 740 1987
Here's the question. I upgraded to e-codes, and did the following - but still get a bulb failure light. I used the passenger side wiring as the main run from the headlight switch. Instead of just cutting off the driver's side, I bought extra wire and ran a length from the high and low beam across the car and spliced each wire respectively with it's match on the passenger side. In simple terms, the two lows are now joined and the two highs are now joined and each pair goes into the respective high/low relay. Why do I still get a bulb failure light? I thought this would only come on if I disconnected one side. I plan on just pulling the dash bulb - but need to make sure that's OK I just remembered that my running lights and turn signals have exposed wiring. Would this trigger the light on the dash? > Here's the question. I upgraded to e-codes, and did the following - but > still get a bulb failure light. [quoted text clipped - 10 lines] > on if I disconnected one side. I plan on just pulling the dash bulb - > but need to make sure that's OK > Here's the question. I upgraded to e-codes, and did the following - but > still get a bulb failure light. [quoted text clipped - 10 lines] > on if I disconnected one side. I plan on just pulling the dash bulb - > but need to make sure that's OK OK, let's assume that the green wire drives the low beam on the left and the green white wire drives the low beam on the right. As long as the two separate wire are running the lights then the current required for each wire is approximately the same. Inside the bulb integrity relay the current on each wire is compared by running it through each wire's own personal coil that is wrapped around a normally open reed switch. Each coil is wound in the opposite direction of the other. When the current flow is close to identical the magnetic field induced by each coil is cancelled by the other; the reed switch remains open and the bulb failure indicator light stays unlit. In your system one coil is unpowered and the switch closes showing a false positive. The same thing applies for the two bulbs in parallel on the white-blue wire on the left and the white-red wire on the right for the lows beams. The relay is biased internally to compensate for the extra load from two filaments. Bob  SignatureThe goal when driving is to miss the maximum number of objects. Aha! Makes perfect sense. Gracias Amigo. > > Here's the question. I upgraded to e-codes, and did the following - but > > still get a bulb failure light. [quoted text clipped - 29 lines] > > Bob > Here's the question. I upgraded to e-codes, and did the following - but > still get a bulb failure light. [quoted text clipped - 10 lines] > on if I disconnected one side. I plan on just pulling the dash bulb - > but need to make sure that's OK Did the bulb failure light come on before you did the work? I wired mine similarly and the indicator works properly, it's actually very nice to have since it tells you if you have a rear light out. They can be finicky when they get old though, dirty contacts in the taillights, bad ground connection, and the solder joints within the sensor itself crack sometimes. It did come on with no bulbs in the headlights and only the running and turn lights in. The turn and running lights had bare wire. I applied liquid electric tape, it still came on, so I pulled the bulb from the dash. > > Here's the question. I upgraded to e-codes, and did the following - but > > still get a bulb failure light. [quoted text clipped - 17 lines] > ground connection, and the solder joints within the sensor itself crack > sometimes. > It did come on with no bulbs in the headlights and only the running and > turn lights in. The turn and running lights had bare wire. I applied > liquid electric tape, it still came on, so I pulled the bulb from the > dash. The turn and running lights are not monitored by that sensor, if it comes on with the headlights unplugged then the problem is with the taillights. Bad grounds, dirty sockets, mismatched bulbs, those are the usual problems. Interesting, thanks. I need to inspect those, check the brake light on the back dash and see if I have an issue there. Thanks! > > It did come on with no bulbs in the headlights and only the running and > > turn lights in. The turn and running lights had bare wire. I applied [quoted text clipped - 5 lines] > taillights. Bad grounds, dirty sockets, mismatched bulbs, those are the > usual problems. |
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