DodgeCoronet.com

Folks, Don't trust your OHM meter to tell you anything useful about your electrical system. Your OHM meter is . at best, powered by a 9 volt battery. The OHM meter works by powering the test leads and then performing a voltage drop test between positive and negative. It takes a single strand of wire to carry the current that the meter can put out. This DOES NOT tell you that the circuit can actually handle any real load. The best way to test any automotive circuit is UNDER LOAD, using the voltage drop method. Basically if have a powered 12 volt circuit, all of the voltage should be used up by the load (say a light bulb). If you took a volt meter and put one lead on the positive battery terminal and the other lead on the positive wire to the bulb, the meter should read zero. This indicated that no voltage is being "used" getting to the bulb. Now if you moved the leads to either side of the bulb, the reading should be equal to battery voltage indicating that all of the voltage got used by the bulb. If the voltage is less than battery voltage ( and the bulb is not full brightness) move the leads to the ground side of the bulb and the negative battery terminal. Let's say your bulb used 10 volts, and the poor ground used 2 more, fixing the ground will leave 12 volts available for the bulb and you'll get full brightness. It is possible that an OHM meter would lead you to believe there was nothing wrong with the ground circuit. Here's a very simple video I found online http://www.youtube.com/watch?v=R6Z-hWzIgDY

Thanks for the automotive electrical 101 lesson, Sedanman67!

I wouldn't say USELESS. Misused would be a better way to describe it. You seem to me to be a very educated person on automotive electrical systems. I can't believe for one second that you would just throw a component, like lets say an ABS speed sensor, at a vehicle just because it had an open circuit code with out first OHM the sensor to be sure that was the problem. Chances are if a sensor ohm with in spec it's not the problem, and it's time to look eles where for an open. More times than you could imagine I get vehicle from other shops in, because someone just threw parts "That didn't fix the problem" at it. When all that had to be done was look harder at harness. Unplug harness (at both ends) and ohm out power wires to ground to be sure they are not shorted to ground is a common practice. JMO

Drag-Net, I stand corrected, "useless" is probably an overstatement. In the example you gave yes, an ohm meter would be helpful, I made my statement in reference to the way many people get mis-led by their ohm meters into thinking a particular circuit is just fine and dandy when there is a voltage drop. I will stand by this statement that the best way to test any load bearing automotive electrical circuit is under load. Also, the target audience here doesn't have any ABS sensors on their Coronets.

Sedanman, With that being said, I will now agree with you about an ohm meter being mis-leading to an untrained user. Have great one.
Danny