gt coupe rev guage fault

Hi, Just bought an early 1990 gt coupe,

There where many faults on the car and have sorted nearly all of them aprt from the sodding

rev guage, thing is it works initially, but only sometimes.

if it works straight away in about 10-15mins it turns off.

not just the rev guage but the warning lights disappear aswell. I'm confused

if anyone has any idea please give me a shout

i have checked a majority of the earths and have even supplied a new earth point just to see.

no luck!!