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How to Test a Coil?


Doc Hawk

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I have a no start condition on my 72Z that was running normally when I drove it last week. The full story is here (all help on that thread appreciated).

 

In an effort to eliminate possible issues, how can I test my MSD Blaster 2 coil? Should I have 12V on the red lead when the key is "on"?

 

Thanks,

David

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If you're not using an MSD ignition box, yes you should have 12V on the positive connection with the ignition switch turned on.

 

Pull out the installation instructions for your coil or look on www.msdignition.com for the owners manual which should have the specifications of the what the primary and secondary coils should read for resistance. You will need a decent DMM for these tests.

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Well, testing the coil will probably be a moot point now. I just found that my entire car is shorted. 12V across the negative battery terminal at all times, even when the car is off, key is out, and all fuses are removed from the main panel. I have started unwrapping my main wiring loom and I'm going to try to trace it, I guess. Everything has current - I can get 12V from the negative terminal to the body, the engine, the alternator casing, etc.

 

Is there a list of "most likely suspects" for a dead short like this?

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Well, testing the coil will probably be a moot point now. I just found that my entire car is shorted. 12V across the negative battery terminal at all times, even when the car is off, key is out, and all fuses are removed from the main panel. I have started unwrapping my main wiring loom and I'm going to try to trace it, I guess. Everything has current - I can get 12V from the negative terminal to the body, the engine, the alternator casing, etc.

 

Is there a list of "most likely suspects" for a dead short like this?

 

Is this with the negitive terminal disconnected from the battery?

 

If it is, then that's normal.

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Yes, the neg terminal is disconnected. How could that be normal? Doesn't that mean that there is a 12V draw at all times on the battery? I thought that there should be no draw when the car is off. My primary test was by disconnecting the negative terminal on the battery, then bridging the gap between the neg cable and the neg terminal with the multimeter. That reading was 12V, which says to me that even with everything off I have 12V flowing throughout the car.

 

What am I missing?

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Yes, the neg terminal is disconnected. How could that be normal? Doesn't that mean that there is a 12V draw at all times on the battery? I thought that there should be no draw when the car is off. My primary test was by disconnecting the negative terminal on the battery, then bridging the gap between the neg cable and the neg terminal with the multimeter. That reading was 12V, which says to me that even with everything off I have 12V flowing throughout the car.

 

What am I missing?

 

 

I replied to your PM, let me know if that helps clear up why there will be 12V shown on teh negitive terminal with it disconnected from the battery.

 

Simply, yes there is always a small drain on the battery with the battery connected to the car.

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