I had to replace the bulb holder on one of my wagons. Plastic piece with circuits and sockets for the various bulbs. I think it was about $40 online but don’t remember the source.

 

The bulb works fine when I move it to the right side. Makes me think the assembly is ok.

 

The left and right marker lights have separate fuses. Does your front left parking light work? It's the only other lamp on that fuse.

Fuse 23 is for the left side. The fuse is downstream of the headlight switch. Check for voltage on both sides of the fuse with the headlights on. (Use a fine-tipped probe or paper clip in the holes in the back of the fuse.)

 

The fuse is ok. The brake and tail light are in the same bulb. Brake works but not the tail light.

 

The brake and taillight are indeed the same bulb, but it's a double filament bulb, effectively two bulbs in one. You can see the two filaments through the glass. The heavier one is the brake light (higher wattage). Also notice there are two contacts on the bottom of the lamp, plus the shell, which is common to both filaments.

The brake lights are all on one fuse (13). The parking lights are on two separate fuses, one for left side (23), one for right (22) (as with all European vehicles). The license plate lights are on their own fuse, as well (4). So, you can easily have working brake lights but not parking lights.

Ref: Bentley schematic 1.

 

Thank you Fresco. So, what might be the problem for having the brake light but Not the tail light?

 

Could be:
* Burned out bulb (but not if the parking light filament lights on the right side). The two filaments (brake and parking) will burn out separately.
* Blown fuse 23
* Burned out front marker light where the bulb has shorted internally, thus blowing fuse 23
* Incorrect or incorrectly installed bulb. The correct bulb has the two tits at about 150°, not 180°, and they are at different heights. This should prevent the bulb from being installed wrong, but with enough force it can be done. An incorrectly installed bulb usually connects the parking light contact to the brake light contact. That connection will cause the parking light circuit to try to light the brake lights, but that will pull more current than the parking light fuse is rated for, so the fuse blows. The parking light filament will light when the brakes are applied, but that's no good, of course.
* A wiring fault, either a short to ground (which would blow the fuse) or a broken wire. This is the least likely scenario, unless the car has led a rough life.

 

Thank you for the reply Fresco. I double checked the fuse. It is ok. Still, the brake light comes on but not the tail light. I don’t understand how it is possible in the same bulb.
When I installed that socket assembly on the right, the tail light came on.

 

Such a simple problem yet very challenging to fix.
I don't have any other suggestions other than check to make sure the wire termination inside that blade plug isn't pushed back out of the molded plug. Also check all of the metal pieces that look like a circuit board are stuck to the plastic housing. Those things are just stuck on there by the plastic being melted at certain points holding it in place. I know it's not very likely at all but...
Also check all those metal pieces to make sure none of them are cracked. That metal is pretty cheesy and I had one that was cracked on my wife's 2003 GLX sedan.

 

Sounds like you ruled out the bulb or indeed the whole tail light assembly. FrescoGreen 01.5 mentions that fuse #23 should be hot when the tail lights are set to turn on. Check that thing with a DVM: both sides of the fuse should have 12V to ground with lights switched to ON.

 

Does the left front marker light work? It's on the same circuit.

Did you measure the voltage at the fuse? Both sides, with fuse installed, lights on, other meter lead to ground. Edit: a test light would be fine, too, if you don't have a voltmeter.

 

Hello again,
I measured the voltage. 11.7 V. Yes. The from left blinker works. I will double check the wire connection to the clip.
What is strange is when I swap the whole socket unit to the right, everything works ok. So, I want to rule out the bad bulb and the socket panel.

 

So the break must be somewhere between that fuse and the tail light connector, maybe right at the connector as AndreasPassat suggested.