Killed two Autometer tachs...no idea how

[Whizbang]

So i got the FB running, and for the sake of seeing my RPMs i decided to run an Autometer tach. Simple wiring seeing i wired the MS up without issues. One switched 12v, 1 ground and 1 tach signal wire. Nothing special. Ran the tach signal from the Neg on the trailing coil. Have it set to 4 cyclinder.

The first tach worked fine for a few minutes. Put the ign forward, it saw power, set itself down to "0" then when i cranked it registered. Fired it up read properly. Then it became out of whack, then it stopped moving and then it did nothing. Thought it was in the wiring. Check everying, and its normal. Returned the tach to Summit (live close by). Got another.

Installed it. DID THE EXACT same thing. SO. I am stumped. Really have NO idea what could be causing this. I am going to run wires from all new sources for the next tach and hope summit will take this one back too.

[RX-7 Chris]

Your car is possessed!!!!!!!!!

I really have no idea what could be wrong.

[rx4ur7]

With all the electrical issues you are having with this puppy keeps making me say - grounds. There has to be a bad or missing one somewhere. Get that wiring diagram downloaded and recheck them all. Check connectors for pulled out wires or corroded ends also.

Electrical gremlins will almost always lead you to ground. Even those that "look fine". Take them all apart and douple check to make sure they are making good contact.

On the 2 and 3 we had a lot of problems with the connectors, most all were aluminum. In Jersey it was salt, Tucson extreme dry then extreme wet during monsoon. And add 115 and aluminum electrical wiring or connectors. Normal part of annual was to take all main electrical harness apart to check connections. Anyone remember the aluminum main starter battery wire?

[Whizbang]

i am beginning to think its electrical as well. I have been having some issues with the MS regarding how some sensors are reading.