Brake lights

[StephenVA]

There is A common issue of the wires in the rubber boot between the body and the tail gate being pinched and fraying. Pull off the boot (actually pull it down) and check to see the condition the wires are in.
This maybe the source of the issues.

Common on those vehicles where the trunk is opened and closed a LOT.

[Eggert]

Originally Posted by trader4

I also presume you're sure have the right connector pin and wire?
Wire is the right color, as determined from Bentley or similar? I guess
you could also figure it out by process of elimination. It's probably the
same color wire as on the other side too.

It was obvious which one was ground, and two out of the three remaining pins gave electrical current when supposed to (turn signal, daylights). Fourth wire was dead.

[upallnight]

Originally Posted by Eggert

Thanks for your willingness to help jd.

But when I unplug the taillight and measure current from the 4 pin plug, (one ground and 3x + for each light; daylight, turn signal and brake light), I only get positive current for the turn signal and daylight. None for the brake light. So logic tells me it has to be something other than the taillight itself, right?

Did you have someone step on the brake pedal when you performed this test? Current is only present if the brakes are actuated.

[Eggert]

Yes, I did. This issue is still unresolved and I strongly suspect the brake light wire (somewhere) to be damaged...

[jdstrickland]

Maybe I was thinking of the running lights getting different fuses. Sorry. I do not have the Bentley manual for my X5, so some of the things I say are said because the E36 and E46 do stuff that can be assumed to be done the same way on the E53.

The left and right side tail lamps are on different fuses, not the brake lamps.

[jdstrickland]

The BRN wire is ground.

[upallnight]

There are tools available that will allow you to trace a wire to determine the location of the break. It sends a tone signal through the wire and you have a receiver that can pickup the tone. If you are not a professional mechanic or not a hobbyist car guy, it would probably be cheaper to take it in and have a technician locate and repair the broken wire rather than spend the money on the tool.

https://www.youtube.com/watch?v=Y0HjaR0tj7Q