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August 12 2017 at 5:32 AM
Gerry  (Login gerryproctor)

Response to So, let me see if I'm getting this right Gary, if I connect the volt meter ..........

You want to read voltage drop, not system voltage. Taking it from your question: "So if I connect the volt meter between the starter at the batt connection, and the battery, lets say at this point I'm getting 12v on the dot...": If you connect the leads as I describe to that part of the circuit and load the circuit by cranking the engine, and there are no issues, you'd see zero or near zero on the meter. If you saw 12v, then that would mean total system failure, in other words, all of the current is being lost to resistance. Again, it's important to test only a specific part of the circuit; battery positive with the meter's positive lead and the meter's negative lead to the first point of contact in that circuit path. Connected this way, and with no load of the circuit, your meter will show zero voltage. If you put a load on the circuit, like cranking the starter with the ignition disabled, you will see a small voltage on the meter. There will always be resistance in the circuit and you're trying to see how much.

If you want to test this on a smaller circuit, hook the meter from the battery positive to another terminal, like the positive terminal at the headlight plug at the headlight and turn on the lights. Again, you're not going to see system voltage, but how much voltage is being lost.

You actually have to connect the meter as I described to see for yourself how it works. I know it doesn't seem to make much sense since we normally test circuits for voltage presence or continuity.

In testing the way you're describing the outcome, you'd be testing the complete circuit -positive to negative. With a good battery and an unloaded circuit, it will always show full battery voltage. And, as you likely know, once you put a load on the battery, by cranking the engine, voltage will always drop based upon amp draw. A starting system is going to pull around 150-200 amps and will momentarily draw the battery voltage down to around 11.5v or so. You can get about the same information by testing for system amperage with either a high capacity shunt or an amp clamp but then you'd have to know what a healthy system's amperage draw is supposed to be to know if there's a problem.

And as others have pointed out, good grounds are necessary.

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