Flicking rpm counter with engine off

[antant]

Hello All,

My first post.

My rpm counter occasionally flicks up and down when the engine is off. It always happens when I plug in my 12v/230v inverter. But I also have a fake LED alarm light which may also cause the problem.

Works fine when engine is running.

Thanks,
Ant.

[davepoth]

It's wired wrongly. Fault check it - Does it happen with the invertor removed?

[antant]

Thanks for the reply.

It does not flick all the time. But when the invertrr is plugged in (cigarette) it does every time.

This was happening before I got the inverter and only really noticed it when I fitted the alarm LED.

What do think is wired wrong the RPM counter?

[annodomini2]

I'd say it was a duff inverter more than the Tacho, sounds like the ground is floating due to the inverter.

Or backfeed signal noise into the ground.

[fergus91]

how far is it moveing? is it just like twitching or going round the whole rev range.
ive seen a car with a twitching rev counter (race car so less electronic stuff to cause problems) what caused it was the ignition being on causeing the fuel pump to cut in ocasionaly and droping voltage