Bought a 1.8lt Insignia abot 6 weeks ago, when i came to switch on rear demister nothing happened. looked on the internetand everything pointed to the module in the tailgate (aerial booster) why that has to do with demister i am not sure. I removed rear trim but there was no module, someone had removed it and fastened wires together. TRied fitting module but still not working, no power to module at all.

Can someone tell me why radio booster and rear demister go through this module, it makes no sense. 

I am stumped hopefully someone can help, thanks in advance

Hi John.....welcome to the Forum

It is possible that the current is shared by both items, assuming it can be switched independently.

I would start by first checking the fuses to see where the power is going off to an also check the wiring near the screen