Heated Rear Window Problem.

My heated window doesn’t work. I have 12v at the window and there is continuity so l know the wires in the window are ok. But if l unplug the earth to the window, the brake lights come on, so l assume l have an earth problem.
Can someone offer guidance on where to look, or have any of you had this problem?

my money is on the earth however what landy do you have etc

It’s 2004 Defender 90. I’m sure it an earth problem, but l don’t know where to look.

Look behind the cover in the OS rear corner of the tub. [ presume 2004 is similar to previous years ]

I’ve check the earths and they look ok, but I’ve sussed out how the brake lights are getting power. The heated window tracks share the same earth as the high level brake light. When l switch on the heated rear window (although power is going to the window) it doesn’t work, but if l unplug the shared earth on the window the brake lights come on, is this normal?

Sounds to me like the earth you're unplugging isn't very good