Hi all. Driving 60kph 4th gear 2000rpm on a flat road, tacho needle started to dart up in a floppy wobbly fashion to 2400/2500 then back to 2000. The clutch doesnt seem to be slipping so I'm hoping it's some sort of electronic glitch, worn unshielded wire, leaking magnetic field? It happened once before when I degreased and washed the engine.
Any help appreciated, thanks.

Yep. Seen this too. When wet, the plug leads crossfire and upset the tacho electronics - why or how, is anyones guess. When it happens in the dry, its still a crossfire somewhere. Happened to me in my TP because the high tension lead slipped out of the ignition coil. No power, engine dead, slow to a stop but the tacho was creeping up! Had me stumped until I lifted the bonnet by the side of the road. Maybe check that all your leads are connected properly to spark plugs, coil and distributor cap. If the problem persists examine distributor cap for cracks and internal dirt or moisture. If in doubt replace - if the problem persists replace plug leads. Good luck!

Thanks. I'm going to replace the leads.

Don't replace them just check they are sealing okay! Its fairly cheap ($10) so try a tin of contact cleaner, it just smashes water away and then evaporates before your eyes! Its also handy to have around and will last you a fair while if used sparingly

I think you will find nothing will fix it short of individually inspecting/testing every component from the coil to the dash to the needle.

Its like a needle in a hay stack, I have spent hours and hours trying to diagnose/fix a handful of different dash's doing the same thing, but never once got one to work...

And I am an instrument fitter by trade :doubt:


%&$#en stupid tachos :badgrin:

Replaced the leads and now it also flops down 500rpm. The needle darts around, up and down, like a kitchen scale.