Had an email from the guy today saying:

Right just spoke to peter at stack and he has said its more than likely the gauge that's had it, he said if I send him the gauge and the sensor he will test it for me free of charge just have to pay the return postage and obviously the post there. I don't no what to do as I'm 99% sure it's fitted correctly and should work, I don't really want to be spend money on it as its only another £70 for a brand new one and if it's turns out this ones had it I'll need to buy a new one anyway. What do you want to do? Have the gauge back and refund me or take a chance and send it to stack for testing? You cannot buy just the gauge or the sensor on its own so if need to buy the whole kit of either the gauge or the sensor is faulty. Upto you mate what you want to do.

No, how do i know he hasnt fucked it by somehow wiring it wrong?

It worked fine the last time i used it but i cant imagine it just breaking from being sat in the garage...

I do electronics repair so can have a look, just not sure if i should as i dont know what he has done to it...