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Old 07-27-2021, 08:12 PM
Theodore Theodore is offline
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Alternator question

While working on the cooling system of our 1990 Grand Wagoneer over the weekend, I noticed Im only running 2 belts (courtesy of PO) and with working A/C I have work to do to swap pulleys on both the alternator & power steering pump to get back to stock.

While removing the alternator of unknown capacity, the internal bolt holding the terminal came off. I took it to a local alternator shop who offered to rebuild it to 105a, swap the single for a double pulley, and fix the terminal.

This evening, reading forums Ive seen mention of upgraded alternators causing dash fires; an ammeter bypass, use of a voltmeter, etc.

Our 1990 Grand Wagoneer has a voltmeter stock in the dash.

Question: is a 105a alternator a bad idea given what I have? Have seen that 75a(non-A/c) & 85a (A/C) alternators were standard.
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Old 07-28-2021, 04:07 AM
Theodore Theodore is offline
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Poking around this morning, I found a post that leads me to believe upgrading the alternator is ok, given later model Grand Wagoneers have voltmeters in the dash vs ammeters.

https://www.fsjnetwork.com/forum/viewtopic.php?t=5878
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Old 07-28-2021, 02:06 PM
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rang-a-stang rang-a-stang is offline
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Yep. You should be fine. Make sure the wiring for the Alt is in great shape though.
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Old 07-29-2021, 06:50 AM
Theodore Theodore is offline
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Thanks, rang. Will take a look & re-wire the charging wire/ground according to the 105amp capacity.
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Old 07-29-2021, 10:06 AM
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tgreese tgreese is offline
 
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I looked online for some indication of the proper wire size for this purpose. I expect there is currently a 10 ga wire ("your wire") that goes directly from the "battery" terminal of the alternator to a fusible link that connects to a post on the starter solenoid, where it connects to the battery cable. This is the only circuit that will ever see the potential 125A charging current from the alternator.

This site https://mgispeedware.com/wire-size-chart/ shows a 10 ga wire as ok for 3' length at 125 amps. I expect your wire is about 3' in length, and thus should kinda be ok. You could go up one size (8 ga wire, 12 ga fusible link), but I would not worry about it.

Personally I would not spend a lot of extra money for a high-amp rebuild. The double pulley is what you really need. You can buy a 94-amp version of these alternators new for well under $100, albeit without the required pulley. Keep that in mind. Maybe your shop will sell you a new part with the pulley you need for a competitive price.
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Last edited by tgreese : 07-29-2021 at 10:38 AM.
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Old 07-29-2021, 05:54 PM
Theodore Theodore is offline
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Thanks, tgreese; are a great resource to us seeking to learn; just finished dinner & sat down to research alternator wiring, wire sizes, and fusible links and found your post - had a manna from heaven moment; saved me a ton of time.

On the alternator, I think I did ok; shop rebuilt the alternator from 75a to 105a; swapped pulleys, and fixed the broken terminal for $80, though I think I need run back by for a pulley swap - the distance belts seems wider than the water pump pulley.

Am glad to hear the stock wiring is ok.
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