W123 Rear Light Problems
 

The rear lights on my 83 W123 Diesel are working very strangely. With the headlights turned on when I use the signal for a right hand turn the yellow light on the right blinks as does the red light next to it as well as the white back up light on the left side. The yellow and red blink alternately while the white back up blinks with the red on the other side. Left turn signal works as expected, just blinking yellow lights. When turning on the 4-way flash if headlights are off all is OK, with lights on I get the similar strange behavior in the rear. Wth the headlights on, pressing the brake pedal will cause a very slight glow in the right-turn signal in the dash. Also when putting the car in reverse with the headlights on will cause a bright glow in the right turn signal in the dash which gets brighter when pressing the brake pedal. What could be causing this? Bad flasher unit? Is there only one flasher for both directionals and flashers? Could there be something wrong with the headlight switch? The rear bulbs appear to be the correct type and the cruise control works fine which I know uses the rear lights for signaling. Any advise is greatly appreciated.

Help !
 

Please, can someone take a stab at this. I'm really lost and don't want to just start swappping out parts. Thanks MUCH!!

rmmagow

Man you've got a good one! The real question is where is the problem coming from? Is it one particular area or multiple problems?

I would start with the easy basics: make sure your battery connections are secure and not corroded.

Fuse box: Fuses all good? Corrosion? Can you easily rotate each in its respective holder? Sometimes they look good but are bad at an end. Check carefully.

Next, check all the bulbs front and rear for correct ones and to make sure there isn't corrosion present. This can often create very weird things. Make sure the bulbs are the correct spec. In the trunk, the rear light clusters are easy to take out. Make sure the connector to the light housing is seated and doesn't have any corrosion. the fronts can be disconnected by their gang plug as well.

You can even disconnect lighting modules, such as the right-rear, per above, and try the lights. With one group disconnected, the flasher will flash more quickly than normal

I am taking a guess here that it could be a bad ground cluster, such as under the dash on the driver's side.

It is my understanding that the blinker is driven by one relay.

Does the car have a phone or a stereo that is non-factory? Any additional electrical devices added to the car?

Start with these and let us know.....

Haasman

I had a similar problem so I started by going from the wires coming out of the taillights and sure enough two of them were exposed and they were touching shorting each other out...

First guess would be that you have a short--a live wire shorting to the other lights some where. Most likely place is in or just before the tail light assembly. If that is all perfect, then it might be under the dash (but not likely).

Some Work
 

OK, I looked at the bulbs, one of the 10W 6CP bulbs doesn't look quite right and I'll order replacements for all. On the passenger side tail light connector there is a brown wire leading from the connector to up underneath the plastic trunk liner. I suspect this is going to ground up there someplace. The wire just comes right out of the plug, not into the wiring harness itself. Is this normal or did someone run into my problem and try to fix it. Is the plug that attaches to the bulb fixture comeapartable? I'd rather not break it if possible but I do think there's something wrong in here.
Thanks for all your advise.

The brown wire is a ground. I have forgotten where is goes. Look around, I am sure you'll see where it attaches.

The tail light housing unit can be taken apart. There are a series of integrated clips, part of the black plastic unit that hold the metal "bulb holder" in place.