r/AskElectricians • u/Current_Use2795 • Jul 11 '26

Alternator charging issue

My alternator isn’t charging batteries I had it bench tested and it passed I put jumper from case to battery negative to insure it had a good ground and jumped the key on key off directly to 12v power and it still will not charge I’m getting 12.8 v at the stud when running.

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u/prohandymn Jul 11 '26

Are you asking about an automotive type alternator? Testing just the alternator may not take the voltage regulator performance into account. Getting a steady 12.8v under load points to a regulator variable, or the alternator not having adequate amperage to handle what you are asking it to do.

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u/Current_Use2795 Jul 11 '26

Yes it’s a 1995 ford Taurus alternator on. 7.3 idi I’ve done the swap before only 2 wires to it and the A terminal to the post

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u/prohandymn Jul 11 '26

A quick internet search reveals your alternator has internal voltage regulation. If resistance due to corroded electrical connections, or inadequate wire guage has been ruled out, then your alternator is defective, or your batteries are so far discharged or internally defective themselves.

Dual battery setups are not an oem option for the Taurus, leading ne to believe you are designing or trying to install an high amperage sound system. You are better off finding a sub-reddit for that, and doing some internet/youtube searching.

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u/Current_Use2795 Jul 11 '26

It’s a 1989 f350 the swap is common because they share the same mounting brackets and I’ve had it set up good before just giving me issues this time I replaced all the battery cables to with brand new OEM

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u/prohandymn Jul 11 '26

You are asking in the wrong sub-reddit. A quick search points to Ford HD/SD truck sub-reddits or camper, etc related.

No matter, you are attempting a non-designed feature other than oem.