mk1 golf cabby clocks problem

everytime i have the car running the clocks work the speedo  needle jumps when driving. but when i turn the lights on at night the rev counter/clocks turn off ? any help advice  

On the rear right rocker cover stud - as you look at the car, there should be a brown earth wire. It will probably have dropped into the engine bay.

Re connect it and things should be ok.

Dan

nice one will try that

nice one works now