My rev counter on my crossflow has started acting funny. It over reads the revs most time, but does sometimes give me a good reading. Also, when I flash my main beams with the car off it causes the rev counter to move to 4 000 rpm.

I am thinking bad earth?? But seems strange since it was working fine.

Before I start checking any ideas?

I'd guess at a bad earth too. Thats the first place I'd be looking.

Take it you have got your timing problems sorted if the engine now revs? Did the problem start after any mods? may have some bearing on the problem?

Yes, got the timing right, the tdc mark was out by about 20 degrees. Made a new mark now she runs great.

The rev counter thing is new, and I haven't made any recent changes, but the problem is sporadic which makes me think its an earth problem?

My money would be on the bulb holder in the rev counter being badly earthed. I had a similar thing on mine - swith lights on, rev counter jumps. Try taking the bulb holder out completely first and see if it makes any difference.