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Discussion Starter #1
Hi all,
I put new 75a in with new harness. The black/white wire burned up. I’m reading that I should have upgraded all wiring in car? Perhaps I just order standard stock amperage? Any thoughts ? Thank you so much.
68 390.
 

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The stock wiring is big enough to use the largest optional stock 55 ampere alternator. So there is no way it can handle 75 Amperes. Also, are you sure you have the proper alternator wiring harness? There are two types depending on options. Lastly it is possible to connect the alternator wires improperly.

Any of these three issues can melt the wiring.
 

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Perhaps your engine is not grounded to the chassis very well and that wire was the easiest path to ground for the electricals. I have seen that happen.
 

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Discussion Starter #4
Thank you both for your words and time. Much appreciate. I feel fairly confident my ground to chassis is solid. If I did have the proper harness and connections would the 75 Powermaster alt work or no way it work?
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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I don't think the alternator is "too big". The numbers they put on them are only the maximum capacity. If your car only needs 15 amps to run, that's what it will provide. Whether it's the stock 35 amp, your new 75 amp, or my overkill 130 amp.
Something went wrong and like above, the first thing I would suspect is bad grounding. Second, wired incorrectly, third bad connections with the existing wiring.
 

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The wiring is really fried. Let's discuss the possibilities.

If there was a bad ground then there would be no way to overload the wiring like that so the ground issue is irrelevant. If the car truly uses 75 amps then the stock wiring is not sufficient. To use 75 amps you would have to have an electric fan duo, air conditioning, an electric water pump, and a nearly dead battery. The engineers probably had a 10% fudge factor on the 55 amp wiring, so it would likely survive 65 amps without melting the insulation over time.

Your wiring apparently lost its smoke shortly after hooking up the new alternator right? That indicates some level of operator error. Either the wrong harness or the wires hooked to the wrong terminals.
 
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