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Offline hqtoyou

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resistance testing
« on: September 15, 2012, 03:19:23 PM »
My Multimeter when set on the lowest setting shows approx. 3.0 when I hold the test probes with my hands so I know that it will read low resistance but when I do any resistance checking on my coil posts while out of the car it reads 0.00 and any other values that I try to check on the car as shown in the repair manual everthing read 0.00. Does this mean that my coil is damaged and I have a grounded wire somewhere in the car that may have damaged the coil? My multimeter when set and ready for testing reads 1_.__ then counts down quickly to 0.00 when checking for resistance on the car.

Offline ToniJ1960

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Re: resistance testing
« Reply #1 on: September 15, 2012, 04:21:10 PM »
 ok a few things when youre measuring resistance.

 1. the range if its 1k full scale .oo1 is a tenth of one ohm. A few feet of wire is about that much resistance. If you have some solenoids or resistors (even better) check to see if the resistance shows up correctly on the meter. A 12 vdc solenoid could be around 50-100 or 200 ohms maybe up to 1000 ohms. If youre reading the resistance of your skin holding the probes in your fingers  and the meter shows uner full scale like 300, then youre not on 1k full scale more likely its on 100k full scale or something like that, maybe even 1m full scale then .001 1000 ohms and you wont be  able to measure smaller resistances on that range. Skin resistance is much higher than 300 ohms.

2. if the battery is weak it can give all kinds of weird readings on resistance measurements

3. if theres any residual voltage where youre measuring, it can alter the reading and potentially ( pun sort of intended) damage your meter. Resistance range is the most susceptible to damage this way

 So check your range carefully, check your battery, and use the voltmeter first to make sure theres no (not even tiny) amount of voltage across the points youre going to check for resistance/continuity.

Offline ToniJ1960

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Re: resistance testing
« Reply #2 on: September 15, 2012, 04:28:44 PM »
 one more thing if a dmm has been damaged by voltage placed on it in the ohms mode sometimes the meter can be damaged in a way that makes any resistance show as .000 so its a good idea to check it against a known resistance.

Offline hqtoyou

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Re: resistance testing
« Reply #3 on: September 15, 2012, 07:55:36 PM »
Thank you for the reply. I'll check it out. By the way this all started when I had a rough idle and found out that none of the cylinders are firing  consistently. I've check every possible reason for this and any repairs that I have done to the ignition system has changed nothing at all.New ICM,plugs,plug wires,coil,cap and rotor,pickup coil,distibutor,any elec. plugs that looked bad. There is just no change at all. Also, could you possibly tell me where the resistance wire is on a 1978 pinto?