Rear Tail Light Problems

[wichitaguy57]

1983 SC without a lot of mods. I’m using the Bentley electrical diagram on 970-17. The Reverse lights are OK and so are the Brake lights. I’ll use Park-B to identify the Parking filament of the brake light blub.

A friend notices a difference in my rear tail lights. As it turns out my right side turn signal light is on and it shouldn’t be. Trouble shooting this problem goes down a couple of paths. No left side rear parking lights in Park Mode, the right side rear Turn Signal blub is on with the lights switched on and the right side rear Outer Marker and Park-B are flashing when the Turn Signal is activated. All Front Maker and Turn signal lights are OK.

Readings from the bottom of the fuse panel.

Parking Light Control – Key Off, Light Switch Off, Turn signal Activated
Left side activated - No Side Marker or Park-B
Right side activated – Side Marker, Turn Signal, Park-B are On

Left Rear Parking – Fuse 4 -- 12.24V ** No voltage at the plug in
Left Rear Turn - Fuse 10 -- .08V engine compartment

Right Rear Parking – Fuse 3 -- 1.91V
Right Rear Turn - Fuse 9 -- 4.17 V Should be zero?

Lights On, Key in Run Position – Engine NOT started
Left side – Side Marker, Park-B are on
Right side – Side Marker, Turn Signal, Park-B are On,
License Plate lights and engine compartment light are On

Left Rear Parking – Fuse 4 -- 12. 4V
Left Rear Turn - Fuse 10 -- .12V

Right Rear Parking – Fuse 3 -- 11.91V
Right Rear Turn - Fuse 9 -- 4.28 V Should be zero?

Key in Run Position, Turn Signal Activated – Engine NOT started
Left side –Turn Signal is Flashing
Right side – Side Marker, Turn Signal, Park-B are Flashing

Left Rear Parking – Fuse 4 -- .03 - .40V
Left Rear Turn - Fuse 10 -- 0 – 11.4V

Right Rear Parking – Fuse 3 -- 0 – 9.5V Should be zero?
Right Rear Turn - Fuse 9 -- .4 – 11.25V

The ignition switch died and the PO decide to splice in a toggle switch to activate the starter. The right front marker was removed to install an air scoop. The right rear tail light assembly screws are frozen. I haven’t decided to drill them out. I did remove the muffler to cut off the captive nut once it was no longer captive for the left side.

Parking Light Control - not sure why I’m not getting any voltage to the plug. Voltage to the right turn signal must be coming from Turn signal/ Parking light contact switch or is this a ground problem?

Lights On, Key in Run Position – Turn signal switch is bad or ground problem.

Turn Signal Activated - Turn signal switch is bad or ground problem.

If ground where do you look?

Thanks for reading,
Guy

[wichitaguy57]

I was able to remove the right side tail light assembly screws and the two small screw that hold the rear plate of the assembly to the main body.

The trick I used, not sure why I never thought or heard of it before, was to use my cordless drill in reverse racket mode. Set the torque selector to less than half and after 5 or 6 attempts of about 30 seconds each, the screws broke loose and the captive nuts held.

The inside of the left tail light look great. Clean, no corrosion, no cracks in any of the PCB boards. I'll get to the left later today.

There's a ground behind the assemble to the inside that I'll clean and protect with some silicon grease.

[wichitaguy57]

Finally found the reason why the rear right turn signal was illuminated. The right front parking light and turn signal are connected to the main wiring harness behind the right front headlight. Not sure why, when or who, but the three wires coming from the parking/brake light where plugged into the WRONG connectors. The parking light was going to the turn signal, turn signal went to GROUND and ground went to the parking lights.

Not sure why more issues were not popping up. Maybe because the voltage wasn't going through a fuse? If someone has a comment, please post.

Picture shows the corrections.



When I pulled fuse 3 the rear turn signal that was illuminated, went dead. Replaced fuse 3, pulled fuse 9 and the light stayed on. No voltage at the top, but approx 6 volts on the bottom. Pulled the turn signal light apart and ran a secondary ground and the rear turn signal went off. Then it was a matter of finding why the ground was bad, which in the end, was the connector behind the light.

Too many hours for such a simple problem. I had removed both tail light assemblies and opened them up, check and rechecked connectors. BUT, I learned a ton about the electrical layout of the car.

Somewhere along the way the connector from the head light switch to the head lights became loose so I had to remove the switch and fix that problem as well. Couldn't figure out how to remove the round nut. I didn't realize the rubber housing was molded around the nut. Still, a set of vice grips on the stalk and needle nose vice grips on the nut was needed to loosen the nut.

Now I have to figure out why the left rear parking lights don't working in Park mode.