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Q: Alternator dead short when power applied.

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I have just installed a new 200 amp alternator with a Painless 10120 wire harness. When I check for continuity from the positive battery post terminal to the casing of the alternator or any area of the grounded engine block, I get continuity. So when I hook up the 12v. DC and try to install a 60/70 amp maxi-fuse of course it keeps blowing for I think I am creating a dead short. Is not the isolation post on the alternator where you hook up your 12v to keep the 12v from dead shorting. Why the continuity from positive post terminal to ground areas of motor and body of alternator. There is a specific way the wiring must be done when you install a larger than 65 amp alternator and that wiring I am sure is right. Please, WHAT AM i MISSING. I am supposed to be leaving for holidays in two hours and I need my car. HELP>..... DUNCAN Matheson
My car has a manual transmission.

A: Firstly, with the battery disconnected you ...

Firstly, with the battery disconnected you will have continuity between the positive cable to the ground of the body or engine if you have any components hooked up or have fuses in. You are getting a complete circuit through some of these components. You will need to check to make sure all of the wiring on your power side is not touching ground before going through the components.

Disconnect the big main cable to the alternator and see if the short goes away. If it does, then use your meter to measure the ohms between the alternator post and the alternator case. You should have continuity in one direction and if you switch leads you’ll have no continuity. This will tell you the diodes are good or shorted in the alternator. If you have continuity in both directions then the large post is grounded or the internal diodes are bad.

If you can’t get it to work and you decide to get this fixed, consider contacting a certified mechanic who can diagnose your electrical issues firsthand and fix it accordingly.

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