Quote:
Originally Posted by wstaab
I am going to pull the tach and check the continuity in the connector that mates to the factory wiring. May be a problem with the ground wire in the connector. Wiring diagram says the bulb is internal in the tach.
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And, before you dismiss the problem as being a bad gauge or bad connections in/to the gauge and/or bulb, perform the same test, meaning rev the engine and turn the lights on,
but do the test with the alternator disabled so that the car is running on battery power only. Here's why: If the alternator is putting "polluted current" out, the additional load of the lights increases the pollution. That pollution can affect your tachometer readings. An oscilloscope would show that in short order, but running on battery power only (just revving in your garage or an around-the-block drive with the lights on) is an easy test. This can be a tricky bug to find when you get one -- and Blas's test may or may not point you in the right direction. Here's a YT video on it for those that are really interested: