Hi-all Could anyone help me with a problem. When my engine is on tick over 1000 rpm the rev counter needle flickers up and down and when you rev the engine it stops flickering. If you put the head lights on the rev counter flickers more. The alternator lamp also comes on when on tick over but goes dimmer when the engine is running at normal revs. Ive checked the volts and it is charging at 13.7 volts. Does anyboidy know the cause of this, its just started to happen after the car as been on the road for about 5 months. PS Its a ford pinto, with a pinto alternator. Hope someone can help. Thanks. Jacko.

Slack fan belt, grubby conections in the charging circuit, shorted surge protection diode if you have an ancient alternator or most likely a faulty regulator in the alternator. Light sometimes gets brighter on increased load and revs with the latter.

I hope you aren't suffering from the same burned out rotor problem that I've had with my Pinto with diahatsu alternator.

Sounds like the alternator is on its way out. I had the same with a mk4 Escort and a new one fixed it.

It's not necessarily anything broken, could be just incompatible ignition system and tacho. Try wiring a 5kohm (ish) pot in series with the wire from the tacho to the ignition & see if it can be adjusted to behave properly. If it can, measure the resistance & permanently wire in a fixed resistor of that value. My V8 did the same thing when I changed to electronic ignition.
Bob C

Just re-read initial post, 13.7V and charging light on dimly sounds like dicky alternator.......
Oh yeah - the LT side of ignition circuits leaps around up to 300V so it might give you a surprise if you touch it.
Bob