Tachometer in 1.6TD goes crazy

[maloosheck]

Tachometer in my 1.6TD ('85 CE1 it if makes any difference) goes nuts. It shows some reasonable rpms only when it is freezing cold and I still don't believe it is accurate. Most of the time the needle just stops at full sweep. I noted the bumpy road can bring it back to the operating mode (indicating reasonable rpms) or switch back to full sweep.

I have already replaced the voltage regulator at the back of the instrument cluster. I have also cleaned the connections between the alternator and the cluster.

Is there any way to locate the issue with the multimeter? I understand that W terminal should be at 8VAC from what I found here.

[bajacalal]

It sounds like you have something wrong with your instrument cluster.

I would take it apart and clean and tighten all the contacts that you can find, not just the ones at the plug, but the ones on the printed circuit as well, where it connects to the tachometer and, if you can get to it, take a look at the tachometer circuit board for any loose components.

[maloosheck]

That's what I did today. I disassembled tacho down to the PCB inside, but did not note anything loose. After I reassembled everything back, I started engine and (surprise, surprise!) it was showing some idle rpms. Will see if this helps permanently.

Now, about that idle: it is going up and down depending on the lights being on and off... Is this normal?

[RabbitJockey]

That's what I did today. I disassembled tacho down to the PCB inside, but did not note anything loose. After I reassembled everything back, I started engine and (surprise, surprise!) it was showing some idle rpms. Will see if this helps permanently.

Now, about that idle: it is going up and down depending on the lights being on and off... Is this normal?

That's normal.  Sometimes just resembling stuff helps,  if not its still and easy fix cause sometimes the traces go bad on the membrane so u just gotta run a wire straight to the signal post for the tach.