Quote:
Originally Posted by Bill Hanlon
Another way to look for a high resistance ground path is to use your DVM on a DC low voltage scale. Turn on all lights, radio, etc and have the engine running. Put one probe of the DVM on the negative post (not the negative cable) of the battery, then use the other probe at various places that SHOULD be at ground. Any reading more than a tenth of a volt or so is telling you that the ground connection isn't all it should be.
You can also use this method for testing for poor connections in the starter circuit. Leave the probe connected to the battery negative post. Hold the other probe against the starter case at a clean, bare of paint, spot. Remove the coil wire then have a helper turn the key to the start position. Voltage reading should be less than 1/2 volt. If not, the engine is not properly grounded.
Now move the battery probe to the positive post. Move the other probe to the large lug on the starter solenoid nearest the starter motor. Have the helper turn the key to start. Voltage should be less than 1/2 volt again. If not, move the solenoid probe to the other large lug on the solenoid. Hit the key again. If voltage is now less than 1/2 volt, the solenoid is defective. If you are still reading move than 1/2 volt keep moving the probe back towards the battery until you get a lower than 1/2 volt reading when spinning the starter to indicate where4 the high resistance starts.
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Yes, this is good advice. Voltage drop is a much more reliable indicator than resistance for checking grounds. You just need to be sure the loads are there as you describe.
Accurate resistance readings anywhere close to zero are typically done with 4-point measurements and handheld volt-ohmeters aren't usually set up for that. A budget voltmeter can read millivolts with good accuracy... but half an ohm... not so much! And even a good solid mechanical contact will have measurable resistance... like 0.1 to 0.2 ohms... so zero is not even a realistic indicator.
Your method also checks out the conductors, which is a big bonus. You can have great contacts on a wimpy conductor that drops too much voltage.