I kinda think I need help. I have had an 82 300D turbo, now has 240,000 miles and generally runs good. My current problem is a crazy tachometer.

Recently, I replaced the OEM trash can tachometer amplifier with the one with the blinking lights. It worked very well for a while, and from reading other posts I don't think it is at fault.

My problem is the tachometer needle jumps in time to the turn signal indicator and pegs all the way when the horn is sounded. Then sometimes it will fall to the bottom (0 rpm) and stay there. At the same time, I will lose air conditioning (blower and compressor?) as if the number 8 (or possibly 6) fuse has blown. When I pull the fuse, it is fine and usually everything works after I put the same fuse back in the fuse box.

The other instruments in the cluster work fine. The hazard flasher does not cause the tach needle to jump. All turn signals, headlights, radio, etc seem to be doing what they are supposed to be doing.

I have seen lots of info on the horn issue but nothing on the turn signal, and some on the A/C issue but nothing I can point to and say "that is what mine is doing".

I have tried putting an old style tach amp in and still get the same needle jumps with the turn signal. I have tried replacing the socket the tach amp plugs into with no improvement. I have tried replacing the multi-switch with one from my parts box, no change. I have added another ground wire from the back of the instrument cluster to the frame; no change.

Since the car is an 83, I don't think I have an OVP fuse.

I have lived with it for a while, but the A/C issue is new and it still gets hot in west Texas in September.

Any helpful suggestions would be appreciated as I have no good ideas left about where to look to track this down.

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