On my 85 300D I seem to have acquired all of the following electrical issues at once:

• Passenger-side front parking light does not illuminate when the parking lights are turned on. However, the front right turn signal light does work (shared bulb, see more below)
• Passenger-side rear parking light does not illuminate when the parking lights are turned on.
• Right turn blinker only works when the brake pedal is not depressed. If I move the turn signal lever to indicate a right turn, the blinker function works until I press the brake pedal. If I release the brake pedal, the blinker begins functioning again.

All bulbs have been replaced with new bulbs and the problems persist. I find it odd (or telling) that all of the problems are on the "right" side of the car (passenger side).

Most electrical questions on this forum are directed to grounding connections; Does anyone know where a possible common ground point for all of these functions may be located? TIA.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

Problems 1 & 2 sound like a bad parking light fuse - they are fused per side.

Problem 3 sounds like a grounding problem, I'd start by checking the ground for the fixture at the back of the car It sounds like that turn signal is grounding through the brake lamps - when you press the brake the ground "goes away".

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

Problems 1 & 2 were indeed a blown #1 fuse. The rear tail light bulb on the right side was "blown" out when I removed it (glass blackened, glass loose from the brass base). I guess it took out the fuse when it went. Added bonus, all dash lights are on this fuse; now they all work again! Thanks for the suggestion.

I'll get to #3 tomorrow. The PO has replaced the entire tail light housing due to a previous accident, so I'll need to check the housing and all the internal wires.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

OK, so I disassembled the right-side tail lamp/lens assembly. About twelve months ago I added the second brake light kit to this car. This kit uses the unused light socket to house another brake light. The electrical connect is attached to the existing brake light wire. I guessed that maybe I had introduced a problem when I made this modification.

I took everything apart, did a quick inspection, found no issues, twisted the turn signal wire in the connector to run away from the brake wire (they are adjacent in the connector), tidied everything up, wrapped the wires in black electrical tape and re-assembled the light bar.

Same result. But this time I had a daughter operate the turn signal and then press the brake pedal while I watched the lights at the back of the car. When the brake pedal is pressed, both of the brake lights illuminate, the turn signal light dims and stays on solid. All illuminated bulbs at this point seem to be at about 50% brightness. When the turn signal is turned off, the brake bulbs get much brighter. If the brake is released and the turn signal is on, the blinking bulb is much brighter.

There is a brown wire running from the tail light bar connector to the rear fender, but it is OK. Unless someone has other evidence, at this point I think the problem must be elsewhere. Where should I look now?

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles