Voltmeter Behavior, Verify Accuracy Options

[Superhawk996]

Starting a new thread in response to @emeryGT 350 comment in another thread as follow up

Here’s the background:

[emerygt350]

I think of it more as a dummy light or perhaps a 'general suggestion' about the charging system. However, I have found mine does some disconcerting things that don't allow me to even use it that way. If it's sitting on 12 that scares me, but then I check the voltage and its 13.4. another day it will be at almost 14 and the voltage will be 13.6. That's not helpful. The original lines to the gauge now operate a relay which has a direct (fused) connection to the battery. Hmmm.... I should double check my ground shouldn't i?

[Superhawk996]

I should double check my ground shouldn't i?

Yes! Especially since you’ve previously had issues with the starter & hot starts.

A bad negative battery cable from Batt negative to chassis will cause all kinds of grief as will a bad ground strap from chassis to transmission. The most reliable way to judge the state of these grounds is to measure the voltage drop across the cable while cranking. Visual inspection and appearance is meaningless. Anything more than about 0.2v of voltage drop while cranking is too much - replace the cable / ground strap.

Required reading:
https://www.fenderbender.com/running-a-shop...ircuits-part-11

[Edit] check battery positive cable the same way! Its condition is no less important than the negative cable.


Have you painted your fan shroud or any of the alternator mounting brackets? These are the in the ground path for the alternator.

I’ll get some video of the gauge damping behavior up later tonight. There is nothing in the damping behavior that would explain the variance your mentioning between voltage and/or any sort of extended delay in the voltmeter reporting proper voltage within +/- 0.5 volt.