Rev Counter Erratic on Manual Gearbox Bongo

[Bluespanner]

Rev counter unresponsive when first starts then springs into life after a little bit.
Any ideas ? I'm thinking possible alternator failing, not putting out enough power until revs are at higher levels

Thanks in advance

[Bob]

I've had this twice on other vehicles, alternator both times.

[Bluespanner]

Thanks Bob, yes I think the prime suspect has to be the alternator. Any ideas what the output voltage should be at tick over. I think that would nail it if low

[Bob]

No idea, sorry.

[Flanners]

I have one of those Chinese made volt and temp displays with a USB that fits in the cigarette socket and it shows 14.2v sometimes up to 14.6 on tickover I think anything over 14.x volts is kosher (or even as low as 13.8v+)