Autometer 3991

[Kaskuser Kiss]

EverythingI've read or heard has the coil negative post used for the tach. Until this experience I've always thought tach wiring was a close second to hooking up the battery for ease of installation on these cars. I'm beginning to think I really don't need a tach in the car.

I've been working with RPM with this problem over the past week, and I'm stumped! It should work. What's strange is a separate aftermarket tach works only when the signal comes from the + side of the coil, which makes no sense.

I am trying to understand the break in stand tach. Is this a separate tach, not connected to anything on the car? Typically used for engine evaluation? I thought these hooked up to a spark plug wire, but maybe the one you have is different?

The coil has a + wire to the hot side, usually the ignition switch. It has the - side that goes to the points. I think these can be reversed and the car will work fine. Bob (above) mentioned this. But you mentioned you hooked up your break in tach to the + terminal and it worked fine. This tells me that you maybe have the coil wired backwards. Perhaps you have the + wire going to the points?

If you are using the standard wires, then you have a resistance wire from the ignition switch to the coil. It could be possible the use of a resistance wire will not work with your ultra lite tach. You can try shorting out the resistance wire when the car is running to see if the tach will then work. You can short the resistance wire without hurting anything if only done for a few seconds. Doing so for a long period of time will heat up the coil and eventually it will fail. To short this out, you need a separate wire from the + battery terminal to the coil wire that goes to your ignition switch. Again, verify the + terminal on your coil goes to your ignition switch. With the resistance wire temporarily shorted, does the tach work then?

My guess is that for all this time, you've been running your autometer dash tach connected to the positive side of the coil and probably burned it up. If your test stand tach works, but the autometer doesn't, use the wiring through the dash to hook up the test stand tach inside the car. Still works? If so and the autometer doesn't, I would highly suspect the autometer tach is bad.

Well, my heavy handed son who needs to learn the definition of the word finesse, pulled the 12v power wire from its connection. I checked the wires and they were fine for the first hundred disconnects we made while troubleshooting the tach. After it was pulled loose it gave intermittent continuity readings. The fact that "someone" didn't wire the coil correctly surely didn't help.

You are lucky we don't make you pay for this advise. But then ( to be fair) we would pay you when we give bad advise. As I provide too much bad advise, we better stick to no charge in both directions.

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