Tom Rathjen

Hello.

My tail light warning in the dash is on constantly, although all lights are working. I found this thread: https://rennlist.com/forums/928-forum/461705-tail-lamp-failure.html, and I made sure that I had all the correct wattage bulbs per the recommendation. And still I get the warning.

Does anyone know of a way to jumper the BCU (or disconnect something) such that the tail light warning will be defeated?

This is on an 82 928.

Thanks!

blitz928

Are the rear side markers working too? Sometimes overlooked. You say the tail light warning is on constantly? even with the lights off? Just have to be sure. You may have a failed bulb control module...

Landseer

Good point on markers, they accompany the tails.


If that doesn't work:

https://rennlist.com/forums/showthre...ght=BCU+bypass

I read that by design the 84 BCU is backward compatible with earlier years (reed switch version of same). So this should work for you.

EC928NC

I haven't crawled under the dash on my 82 yet, but on my 85 my big foot pushed the wires off of the brake lights switch down by the brake pedal. If the 82's have the same type of switch.... check the simple stuff first.

Mike Frye

I think the wiring for that goes through the dome light circuit too. I may be wrong, but I'd check all connections.

Also, just because you have the same wattage in all bulbs doesn't mean it will clear. If you replace one you should replace them both. The system triggers the warning light if there's a difference in resistance between one side and the other, so corrosion can be a factor as well as new vs. old. Replace in pairs.

Also, clean all contacts and grounds.

Good luck!

VehiGAZ

I get this warning periodically - maybe a couple of times a year. The PO told me that there was some wire running across the back under the rear carpeting that was causing it, but I've never bothered to exorcise that gremlin...

blitz928

That's right ,check connections and condition of the wires in your hatch under the carpet near the base of the tool kit.

bigmac

Check the grounds also

Alan

YES you are wrong on that!
Good points

Mrmerlin

there is a ground connection point under the rear quarter cover this is accessed by removing the tool cover and the hold down screw on the rear side of the right quarter cover, since the hatch seems to leak water will get into this connection and foul it up might be worth a check ( the ground is kinda behind the rear side of the right tail light assembly) use care when pulling back the cover as it will sometimes crack due to old age and being brittle

Tom Rathjen

Yes, the side marker lights are functioning. I think they have the correct bulbs. but I can double check. Regarding whether or not the warning light is on constantly, here is exactly what it had (emphasis on HAD....more in a moment) been doing:

When I start the car, the central warning light comes on after about 10 seconds or so. Then, a few seconds after that, the tailight warning comes on. (And then I can press that central warning light button to clear it, but the tailight warning stays on.) This happens with the lights off. Then....if I turn the lights on, the warning goes away for 10 to 20 seconds. Then the central warning comes on again, followed in a few seconds by the tailight warning light. Turning the lights off causes this behavior to repeat. So....that is what it has been doing ever since I got the car in May and have been gradually bringing it back to life.

HOWEVER.....for the first time today, the warning never came on while driving the car around in the morning. And it stayed off even after stopping and starting the car on short errands. But...alas, the original behavior returned later in the day. In the evening there was "no warning" again, and then at night it was back.

So....as of today something is intermittent (although it had been a very steady failure for months). I will double check the correctness of the side marker bulbs. Shoot, I'll probably just put new ones in again. I have checked the grounds folks suggested previously (I had a lot of electrical fixes to do on the car), so I think they are OK. I'm still suspecting a flakey BCU, which is why I was set to just jumper around the tailight circuit to defeat the tailight warning.

Anyway....thanks much for the link to the thread with the specific pins to bypass. Exactly what I was looking for. I will report back if I find something.

Happy Thanksgiving to everyone!

blitz928

Are your interior lights functioning properly? I had some taillight issues in the past due to a short from the hatch dome light. The taillights are on the same harness that runs along the passenger side.

Tom Rathjen

Yes, I think so. But that's something else I can check more closely. Thanks

Landseer

Taillights are not connected with hatch, other than wires that travel partway together in the bundle.

blitz928

Yes, but the wires are in the same harness, A short in the hatch dome light can cause damage to the wires in this harness causing taillight issues. trust me I just replaced this entire Harness along the Passenger side due to this.