tda1

So I have looked for quite some time and couldn't find a match for the issue I'm experiencing. When I brake my "TAIL" warning indicator comes on with the ! on the dash. As soon as I lift off the brake it goes out. If I turn on my left turn signal it works fine until I put on the brake. When I push the brake petal all the left side lights dim and I get a fast blinking turn signal as if a bulb is out. I've replaced all bulbs and it doesn't remedy the problem. I suspect its a ground wire but am unsure where to look.
Anyone know what might be happening here?
thanks

Wisconsin Joe

What are the actual lights (as seen from the back) doing?

tda1

here is a video:

dr bob

Clean your rear grounds, and also the tail light sockets. That will solve the problem nicely.

James Bailey

The sockets rust out quite often. A common 1987 > problem.

mdkelly1

+3 re: cleaning the taillight socket(s) and harness connector(s).

Might not be your exact symptom, but this may help.

https://rennlist.com/forums/928-foru...long-post.html

jeff spahn

You can rebuild your tail light sockets with a Nissan Qwest (Quest or whatever) socket from the late 90's. There's a thread here on reenlist how to do it when you discover your sockets are FUBAR.

https://rennlist.com/forums/diy-subm...eferrerid=6055

dr bob

This is a ground problem. Current is circulating between the loops, so the warning box doesn't see the full load on the lamp. The turn signal circuit has the same issue, pushing the other way. Both circuits expect the lamp shell to be grounded. His isn't. Could be the bilb not seating in a corroded socket, or the ground connection from that socket to chassis. Fix both, problem solved for sure. Thw Quest/Ford socket will help with a corroded socket, and I might lean towards that option. But you can find where the ground is open with a DMM, looking to see if there's voltage at the ground terminal of the harness connector. If there is, the connection at the body is dirty. If none, it's likely the socket.

tda1

Yesterday I removed the light assembly. I checked every bulb and socket. There is no corrosion or rust present in any of them nor was any of the bulbs improperly seated. This afternoon I will try the DMM once I learn how to use it
Thanks Dr Bob

mdkelly1

Did you clean the tail light harness plug pins and pin sockets on that side?

tda1

Yes David...I took it off and looked at them. One of them looked a little different than the other two so I took some sand paper to it and cleaned it. There was no change.

dr bob

The harness grounds to a screw just under the left rear interior quarter panel.

The DMM:

Ground the black meter lead. Set it to read DC volts. Most DMM's have a 20-volt scale, a good place to start.

Turn the lights on. Your suspect bulb will be a little dimmer than the others. If you have the bulbs out of the housing, find the two-filament bulb and see if both filaments are glowing.

Use the meter red lead, and work to get contact with the ground connection for your suspect bulb. Your meter will show some large fraction of battery voltage. That's current that isn't flowing through the ground circuit connection to the chassis.

Try the wiring at the harness connector brown wires, probing both sides of the connector (car side and local hanrsess side). If you see no voltage on the car side of that connector, it's the harness connector that's not connecting. If you see voltage, continue to the ground connection under the edge of that panel. Meter red probe to the wires that connect to the bolt there. The bolt iitself should be at ground so no voltage. The wires -should- be at ground too. If not, your problem is at the ground connection under that bolt.

-------

Cleaning these grounds and the wiring there is part of a regular electrical maintenance program. Use a brass brush to polish the connectors, the body where they attach, and the bolt itself. They need to be bright and shiney. If the wires going into the ring connections is corroded, consider replacing the connectors with new plated ones, crimped correctly onto fresh copper section of the wires. There are perhaps a dozen of these ground connections on the car, by the way. Each has the potential to cause odd electrical issues as they get even lightly corroded. If you live in a climate where there's humidity, or where there are big swings in temperature where the car lives, corrosion is a bigger concern. Still-cold wires on a warm day invite condensation and subsequent corrosion.

z driver 88t

Has it always done this or is this recent? I would double check to make sure the turn signal is the correct bulb. I replaced my 84 tail lamp based on the database info from Sylvania at the local Autozone which said to use 5008/10W. My dash warning light came on saying light was out, but it appeared to be working fine. Searching RENNLIST I found that the Sylvania database info was wrong and that I should have been using a 5007/5W bulb. Bulb swapped out and problem was solved. May not be your problem, but unlike most cars that just look for continuity to determine if the bulb is functioning, 928s "know" if the wattage is wrong.

tda1

Thanks again Dr Bob. I'll give that a try tonight.
Chris...this has been an intermittent problem which has increased in frequency and more recently has become the new normal. as for the bulbs, I'm sure they are correct. I did however recently change them and the behavior persisted.

Alan

Don't look elsewhere it is exactly as Dr Bob has suggested..

When two separate system interact - that are not supposed to interact normally (e.g. brakes cause a tail light alert) - then it is virtually always a grounding issue. Always start there - find the common grounding point between the systems.

Alan