MainePorsche

Good job Tim. Perseverance pays off.
Google 'canell 928' - you can access WSM's (Workshop Manuals) online. I don't know OB tail lights. If this ground is in a state, consider all the others. This car does not tolerate sloppy grounds. Your next post will probably be your last on the subject.
Best Wishes
Craig

Lovemyevo2

Since I cleaned up those grounds behind the trim in the rear quarter the warning light has gone from being lit intermittently, to being lit all the time (except of course when the brake is pressed). I think it's a rear-bumper-off job to get at the connections into the bulb harnesses. Hoping that these will be in a bad state and it will be problem solved. My research would suggest the bumper off looks like a big job (for me at least). I've found what looks like a good write up on the procedure so will tackle this as soon as I can.

MainePorsche

Sorry Tim, I don't know the OB's and how to remove the light fixtures on them. Can't imagine complete bumper removal to get to the wiring connection by pulling the fixture, but you never know... Someone will chime in.

Lovemyevo2

Before I pull the bumper off to check the connections in the tail light harnesses, which looks like a hassle...has anyone else had any problems with the ground / connection points in this area? If it's all sealed and rarely causes a problem, I might be best spending time re-soldering all the joints in the lamp controller to see if this sorts the problem? Can this go in the oven in the same way that others have recommended 'baking' the cruise control unit to solve any broken connection issues? Tim

Landseer

No solution here, just some more thoughts.

I'd not pull the bumper cover yet.

That is a hassle. My connections back there have generally been tight.
Am assuming you were able to remove the lenses and clean the lamp contacts.

Reflowing bulb comparator circuit might help.


You've got a lot of posts going. Am not sure what you've done / missed when it comes to the base electrical. For me, the process goes better if I clean all grounds, replace all fuses, polish all fusebox contacts first. Bulb warning ground is above fusebox. Central control computer that processes the signal (under dead pedal) is grounded beneath the steering column, underneath, at least on LHD cars. And bulb ground is behind interior quarter panel.

There has been a tech bulletin on a similar issue, in conjunction with headlights, for slightly later cars. Mine happens sometimes with, sometimes without headlights, making it similar to your situation. I've got the symptom on 85 car.

Reading closely the below Technical Bulletin, note that the problem was FIXED after July 11, 1986 production. Though the bulletin covers model years 86 and 87, its possible that this fix could also apply to earlier cars. I don't know for sure. 85 and 86 are virtually same in USA at least, except for 3rd brake light, yet my 85 is acting exactly like the problem statement below. IIRC, the bulb comparator unit for 86,5,4 is the same, and are backward compatible with early cars also (based on another tech bulletin).
Yes, 84 fusebox is old style, but the bulb comparator circuit is the same.

Don't mean to take you out on a tangent.

Landseer

Actually, based on your high beam inop thread, you've got a whole lot more electrical repair needed before you worry too much about this warning light.

Sort that out first, from stem to stern.

Consolidated electrical thread is another suggestion.

davek9

You do not need to pull off the bumper, the connection for the tail lights are behind the rear interior quarter panels, near the back of the car by the tool tray.
From there you can ohm out the connections to the bulb connectors after cleaning them.
If you haven't yet pulled the lamp controler above the computers do so first.

Lovemyevo2

Thanks all for your thoughts. By way of update related to this specific thread, I seem to have solved the stop lamp warning indicator problem by sucking all the solder off the lamp controller board and re-flowing. Visually there didn't appear to be any problems before, but when I started working through all the joints, one was actually loose.
I checked the ground wires Landseer and all seemed to be a similar thicker gauge.
I still get the main warning light pinging on just after startup, but when I press the reset button on the dash it goes out and then doesn't come back on. Is this normal to show that the warning system is operational or is this more likely linked to one of my other electrical problems??

MainePorsche

Tim,
Do you mean the "Stoplight" (red) warning or the "Taillight" (yellow) warning ? The "Stoplight" normally goes on when you start up. Hit the brake and it should go off. I think it is some sort of safety check for you to hit the brake pedal before you drive - if there is a defect in the system it will remain on.

Lovemyevo2

Yup, red stoplight warning comes on at startup and a quick tap of the brake now switches it off (it didn't before I reflowed the lamp controller). It was the main exclamation warning light that was still coming on. It's not now so I will assume this is related to other problems and consider this thread's 'fix' successful thanks to the advice from this forum. Onto the multitude of other electrical issues...

MainePorsche

Good work.

Jchiodi

Resurecting old thread!
Just looking to see how to pull that rear quarter panel off to check the back of the light?? My DS stop light does not light intermittently!!

Bmw635

I had intermittent tailight warning until today when I swapped new taillight housing so I checked the bulbs, sockets, etc... The socket that the light was out intermitently had some rust in it so I cleaned and spray WD-40 to slow the rust. No more warning light.