Killed two Autometer tachs...no idea how
 

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.

Check your trailing ignitor.

how would that cause the tach to fail?

Any tach failure leads to the ignitor. It is a checklist.

The ignitor generates the signal that the tach is measuring. If the ignitor's bad, there's nothing to measure.

Any particular reason for not using the leading ignition for your tach signal?

Try that first; the tach may not in fact be bad.

i have wasted spark for the leading.

shouldn't the take at least take notice of the power running to it?

If you mean that the tach would load down your spark intensity, it shouldn't. It should place only a tiny load on the ignition circuit. Not enough to matter. After all, the tach is made for normal engines that only have one igition system.

With regard to the powering up: that's a good question. Only things I can think of that would kill new electronics that quickly would be severe overvoltage, reversed polarity, or something like that.

well i leave monday for basic, so ill have to figure out when i get more than likely. Im going to redo and add some grounds.

"Simple wiring seeing i wired the MS up without issues."

MS does that mean MSD? You should hook up the tach signal up to the MSD box if that's what you're talking about.

Good luck with Basic. Thanks for your service!

Megasquirt. I have an MSD box but right now the Megasquirt is using its output. But i might split off its signal for the next round of tach