Rev counter bouncing

[Ragonz]

Wondered if anyone knew where to start with this one.

Driving along the rev counter works just fine, however upon certain circumstances it starts acting up

Indicators flashing, rev counter needle bounces up and down in time to the flashing
Power window switch (any of them) held down after window is already fully up/down, rev counter needle drops to 0 (as soon as switch is let go rev counter returns to normal, also does not happen when the window is moving)
So far nothing else seems to affect it

I've checked what gounds I can find (3 next to batteries, 1 at Starter motor, 1 in driver footwell) and they all look good.
Has anyone else experienced this and if so have you managed to fix it?

 

[DIRTBIKEUSA]

Sounds like a short in the wiring at the relay box for your pwr window module and/or flasher module. I would start by reading the body wire harness schematic to see where the wires lead to and if they share routing. Then once you have ruled out simple stuff at the terminal ends connectors and relay Boxs, you would need to start tracing the wire harness.

Since the other affecting systems work normally it’s hard to tell.

 

[NeverFinis]

Does sound like a bad ground. Check the ground at the back of the engine, as well as the ground at the back of the t-case to the floor pan. There are many more grounds in the engine bay. The one at the t-case is where the speed is read for your tach.

 

[Ragonz]

Don't suppose anyone has diagrams of the wireing harness's / ground locations for a 93 1HD-t?