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Don't really know how to use the thing but i had the probe in 12v dc and put one probe on the gas tank and the other to the ground screw for the rear tail ights which is on the trunk latch support. The ohm meter went to zero. When I touched it on the paint it went it all the way in the other direction. Does this mean that the tank and or the tail lights are well grounded?
 

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Here's a decent video for ya Harv: http://www.youtube.com/watch?v=bF3OyQ3HwfU&feature=related

Some meters have needle displays rather than digital - but same diff, just look at the scale correctly

Always make sure you are making good "electrical contact" (ie clean bare metal) Using the ohm function - test your meter first by touching the leads together should be 0 ohms (i.e a "short" or solid conductivity if checking wire for continuity)
 

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AQlso remember not to use the OHM meter on a live circut. Extra voltage may be harmful to the meter.
 

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Zero OHM's means no resistance. Max OHM's lots of resistance. So if I am wanting to know if a piece of wire is good I touch one lead to each end of the wire and it should read 0 ohms if good. Max ohms if bad. Same goes for checking ground.

A note on meter setup. On most meters the 12v would indicate you are measuring a power source that is 12 volts. The ohms setting is independent of the voltage. In fact when measuring ohms the meter runs a small amount of voltage through the connection and measures the drop. That is how it measures the resistance.

If you provide a make and model odds meter I would be glad to loom it up and give you some pointers. When owning a classic car like we do the multi meter will become one of your most utilized tools so get to know it very well!

Hope that helped a little.
 

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Zero OHM's means no resistance. Max OHM's lots of resistance. So if I am wanting to know if a piece of wire is good I touch one lead to each end of the wire and it should read 0 ohms if good. Max ohms if bad. Same goes for checking ground.
To elaborate a bit on Wolfeman's comment;

A wire or circuit may not read exactly zero Ohms, but a "good" connection will usually read a VERY low Ohm value ~ less than 1 or 2 Ohms, depending if there are other components in the circuit. While checking a motor or alternator will give some resistance value of several hundred or maybe even several thousand Ohms - just because of all the windings of wire in the item. However, it should still have an "infinite" resistance to ground (from the casing to the wire leads).

Another good thing to mention is to check is the resistance while wiggling or moving / repositioning the wire run - say, for checking door wiring. The wires might check as "good" when the door is open, but then be "bad" when the door is closed (or vice-versa).
 

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Greer point Mike. Zero is not always zero. Nice catch on the "it worked fine a second ago" saga. Wiggle the wire and watch for changes. I have chased my share of gremlins to find out it was a short I could not see.
 
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