Hi all there;
My car is: 1986.5, 5 speed
I have been chasing this persistent issue with the passenger side taillights.
Symptoms:
Turn headlights on, I get the warning and the passenger lights will not be on (sometimes they may, but most frequently not).
All fuses checked, no blown fuses
If I stick my hand under the tea tray and move it around the bulb control module, the lights will turn on and stay on, but the warning will likely stay on (sometimes will turn off, but most times, stays on).
I changed all the fuses, same issue.
I changed the bulb control module, same issue.
I looked at the rear fender marker (which is in excellent condition and has the rubber boot on, etc and I don't see anything suspect on the cables to suggest fraying/shorting.
I believe that if something was shorting, the fuse would be blown and will need to be changed before the lights would work again, so this cannot be because the lights work

I couldn't care less about the warning if I was absolutely sure that the lights were on, but if the warning is on, I keep having to get bout of the car and check when I am driving it at night
I am at a loss. Any suggestions as of what else should I look into?

Thank you for your help and suggestions
Miguel

 

If moving the unit around caused the light to come on the I’d start by removing the connector to the bulb check unit and clean the pins, if that doesn’t fix it then open up that connector and reflow all the solder joints. The warning is probably being cause by too high resistance on that side so won’t blow a fuse.

 

a few things can cause this
So lets start with the easy things first.
Remove the pass parcel tray,
Then remove the connector from the light check computer,
Pop the cover off the connector and examine the wires,
Look for a cold solder joint, resolder any one of these pins that look questionable.
put deoxit 100 on all the connections before you put it back together.

Get the WSM and find out what connector on the bottom of the CE panel is used for powering the rear lights.
Pull this off and spray with deoxit 100.
NOTE this harness travels along the right hand side of the interior along the inside base of the rocker under the carpet.

Moving to the rear of the car in the hatch area.
Find the 2 white 2 pin connectors in the corners of the hatch floor,
these are for the rear side markers take them apart and spray with D100.
Also inspect the rear side marker bulbs in the sockets for corrosion.
Take the 3rd brake lamp apart and spray that bulb holder put that back together.

While your at it disconnect the ground strap, and clean that connection spray with D 100

Get a small 2x4 block and some PB Blaster and a long Phillips screwdriver.
Remove the RT hatch floor hold down bracket,
NOTE lay on the ground and spray the screws from under the the bumper with PB so they break free.
Remove the 2 screws that hold the aft end of the quarter liner ,
then gently press the rear edge of the liner forward ,
just enough to expose the ground bundle thats bolted to the rear bulkhead.
Put the 2x4 down so it will hold the liner whilst you,
get a 10 mm box wrench to loosen the ground bundle and spray this with D100.

NOTE you dont have to remove the screw unless all of the wire ends are fully corroded,
just spraying the D 100 on the ends it usually good enough to restore the full grounding.
Tighten the bolt.

Next look for the round white connector for the rear light,
this might be tucked under the foam pad thats behind the liner.
examine it paying close attention to the ground wires that are plugged into the barrel.
One of these pins usually has a faulty crimp and the ground wires fall out.
if so remove the pin and solder the ground to the pin then insert the pin into the connector.
take the connector apart and spray the pins and sockets with D 100.
then put things back together,
and see if the lights are working.

Please report what you find.

 

Gazfish: Do you mean to take the cap off the harness that connects to the module? For a second, I thought that it could be the harness, since it almost feels as if I move the harness wire bundle, everything starts working, but the harness wiring doesn't look frayed or even in any kind of suspicious shape.
MRmerlin: Thank you. I will re look at all those and report. I did look at the stuff in the back underneath the quarter liner and it looked so good that I had no suspicion, but I will take a second look.
Any other ideas are welcome
Thank you for a starter to do list
Miguel

 

Yes the plug splits in half and you can check or re solder the wires on the ends of the pins.

 

I will try that too. Thank you!