Re: Question about measuring ground resistance. Proper Method?
An ohmmeter measures resistance by putting a controlled constant current through the circuit and measuring the voltage across it. Then the processor makes the calculation to resistance. This current is very small - milliamps - and any other current flowing through the wire will throw the measurement off. The circuit MUST be powered down.
Originally Posted by gamehawk55
Making low resistance measurements with a 2 wire DMM is inherently inaccurate anyway, because the resistance of the meter's leads is a couple tenths of an ohm and meters are usually +/- 1 digit and +/- some percentage so that last tenth of an ohm is meaningless. And unfortunately, a tenth of an ohm at 20 amps is 2 volts drop, which we care about.
There are fancy 4 wire ohmmeters that compensate for lead resistance, but for our purposes a voltage measurement under actual load is more useful than making resistance measurements of grounds. Pick a good ground point for the neg meter lead and touch the bolts and terminals along the ground wire connections. You should never see more than about a tenth of a volt difference if everything is tight.
1999 Buick Park Ave Ultra
Head Unit: JVC KWHDR720
EQ: Audiocontrol EQL
Front Stage: Hybrid Audio Technologies Imagine 5.25 mids, Morel Maximo tweets
Sub Stage: Boston G3 10", 0.5 cu ft sealed
Amp: PPI Phantom 900.4
Rear Fill: Boston SE953 6X9's