Hello everyone. I recently picked up an '87 928 auto 83k miles. It needs a few things but the one I need to fix first is a problem with the brake lights and reverse lights.
After buying the car I noticed that the reverse lights illuminate with the brake lights... This seems very strange to me and now I'm thinking it has major wiring issues..... Where should start? Grounds, Relays?
I just don't inderstand how this could happen.

Thank you.

 

remove the rear light housings and check that the correct bulbs are installed in the correct slots ,
you will see that the sockets have a 21W or 5W or some other number next to each socket,
you have to make sure both sides have the same bulb.
Its possible that someone has installed a duela fillament bulb and it only takes a single fillament.

The reverse light connection is in the front portion of the spare tire well you should remove the tire and inspect the connections ,
see if the connectors are corroded.

Your elex issues dont sound bad but you do need to evaluate them
as well make sure all of the side markers are working and thet the front turn bulbs are also the same,
go to autoparts store and look for Sylvania bulbs in the matching wattages indicated

 

Turn the lights off and turn the ignition on then put it in reverse to see which bulbs light-up. Make sure the right bulbs/sockets are in the right place. Then start tracing for ground faults.

 

It is most likely a grounding issue. Whenever two supposedly unrelated functions start interacting together in odd ways - suspect grounding issues as a first step. Check the rear ground points.

Alan

 

Thanks a bunch guys! I'll start checking. Hopefully someone was dumb and put the sockets in the wrong places but I doubt I'll be that lucky...

 

Went to auto parts store. According to their computer I need 7506 (single fillament) for stop and 7225 (dual fillament) for tails. Both are wrong and don't even fit. The car has single fillament in tails right now and 7528 and 1157 (dual fil) in stop. One of the stops is out I think so I'll replace it and hopefully that solves something. Anybody know for sure which bulbs I need??

 

https://www.sylvania.com/en-us/appli...el=280&make=76

That shows the same thing. I thought there was another chart at maybe Pelican? but I couldn't find it.

As Alan says, check grounds as they would be most likely cause for separate circuits to light together. If it is a ground, they often will light at partial brightness because they usually end up in series off a common ground.

 

Ok finally got it. I put 1157 (dual fillament) in the stops (2) and 7506's (single fil) in the tails (4) . Now the lights are working properly. No more reverse lights when you brake... YAY

So the Silvania chart is COMPLETELY WRONG. Maybe it is for later model '+93+ 928's ??

 

Now I just need to figure out why my right rear sidemarker is getting no power.....

 

the side marker has a connector along the floor of the hatch it is a white flat connector with 2 wires, usually locted near the rear hatch hold down brackets,

take the connector apart,
clean it ,
use a volt meter to verify power,
if you have power then the connection is bad,
or the bulb.
or the light housing is bad

 

Thanks.. Looks like one end of the plug was missing. I just put new connectors on it and it works now.

 

good job...I need to start chasing gremlins on the rear lights myself