Trying to run down an electrical gremlin. Hoping someone here may have had this experience...

When I press the brake pedal, the light on my rear defrost switch comes on. Release it, goes off. I replaced the brake light switch already, no joy. Any thoughts or advice on what to look at first? This is on a 2001 XJ.

 

Check the hatch harness(es). The wire to the top brake light is probably shorting to the defroster power.

 

This. Common issue with the XJ.

While you're back there, pull the driver's side trim panel off and clean up the grounding wire contact surfaces there.

 

You guys nailed it... If I open the rear hatch I can hit the brake and the light on the rear defrost switch does not come on. Or, if I turn on the rear defrost with the hatch closed, the brake lights come on. :-p

I'll post some pics of the fix once I get in there and look at the wiring. Thanks for the help!

 

One way to check the brake light socket ground (or any ground), is to connect it yourself to ground somewhere, (bat neg), and see if that fixes it. Sounds like it might be grounding back through the defrost circuit.

 

I removed the trim from the hatch, pulled out the wiring, disconnected the plugs. Didn't see any obvious wire damage. Put it all back together and now the problem is gone. It's 3 degrees here today, so I'll wait until it warms up a bit to investigate more.