Vectra strange electrical fault

Rear demister not working. If I hold the button on while driving, after a
few seconds, the speedo and rev counter drop to nothing, let go, they come
back up again. I've removed the demister fuse and relay, and the same
happens.

Looking at the schematics in Haynes, the button and relay are connected to a
"timing" unit. Where is this on the car?

Any ideas about what this fault could be?

Many thanks.

 

bad earth somewhere ?
don't know on the timing unit

mike

 

Timer lives inside the fuse board - called a multi timer - look at your fuse
box. The black multi plug on the right is the timer one. try unplugging
this and then putting it back in.