e46 Tail Light Fix

Following the Wifemobile ('04 330i) one day, I noticed that the brake lights were dim and intermittant, though she was not getting a warning in the car.

When she got home, I checked the bulbs and socket connections. No problem there.

A little searching on the web revealed that there is a known problem with e46 tail light assemblies. There is a metal incompatibility between the socket and the plug on the tail light. The ground tends to corrode at that connection. Unplugging it and reconnecting it helps for a while, but making a separate ground is the fix.

Fortunately, there is a spade connector tab on the ground trace in the tail light. All you need to do is add a ground wire with a spade plug and attach it .

Ground Trace to Chassis

With the brake pedal depressed, I was reading 3-4 volts between the ground trace and a good chassis ground. Yup, a bad ground connection somewhere. Note that I let the brake off to take this picture to cut down on glare.

Ground to Chassis

The Brown wire is the ground. I stripped it back and checked for voltage between the brown wire and a good chassis ground. Zero volts with the brake light on. That means that the bad connection is, as expected, between my two measurements, in the plug connection at the tail light.

Soldering Tail Light

Since I know that I have a good ground at the point where I stripped the brown wire, that is the neatest spot to attach my supplementary ground wire.

Finished Tail Light

Tape it up, and plug the spade connector to the tab that BMW was thoughtful enough to put there, and it is all fixed.

I did both sides, and the tail lights still work fine a year and a half later.

The only thing that would have been nicer would have been to use brown wire, so it would have been consistent with the existing color code.