7078 Alternator

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Nayra Waddles

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Aug 3, 2024, 10:17:57 AM8/3/24

to inmiltato

More background if needed: The 351W is a replacement engine put into a 69 Mustang. I think the engine came from a late 80-early 90s F-150 (someone else did the swap before I got it, so I don't have a specific year). The present alternator works, but the voltage drops enough when I'm running lights, wipers, turn signal, radio, then step on the brakes -- the radio shuts down for low voltage. Thankfully, the car keeps running, but I definitely need more amperage.

It's not an ambulance, or a plow, or a winch truck. Your current alternator (if in good shape) should be able to keep up with a 40-50 amp load, which I'm guestimating is your "worse-case" load you described.

However, as I said - I don't think you need it. UNLESS your "stereo" is of the competition variety that dims lights in neighboring towns and cannot actually be listened to inside the vehicle without hearing loss...

Oh, and make darn sure your battery cables and "D+" lead are not corroded and have clean connections. On a '69 with a donor engine (especially Ford) I'll bet that four-to-five decade old D+ lead is all green copper inside. Your charging loss might very well be in the wires alone. Perform a "voltage drop" test across the B+, D+, and battery ground cables.

As far as I can tell the 7074 number refers to the higher amp 1g alternators (90+A). While the 7078 seems to refer to the lower amp alternators. Then there are variations on the number which seem to refer to the number of grooves on the pulley as well as clock position.

According to -to/interior-electrical/1407-how-to-identify-and-select-ford-alternators/ the 1g, 2g and 3g alternators are interchangeable. You would have to take the voltage regulator wiring into consideration if you did swap 1g (internal or external) to 3g (internal). The site also mentions that there are many variations to the Ford 1g alternator cases.

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