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Alternator help

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I am in need of a new alternator and need some help on what I have and where I should get a new one. Specs are GM alternator on a carburated 502 jet boat. I know I need a marine unit. I know GM alternators are something like 1 of 2 styles but not being a GM guy I dont know what I have. Attached is a picture of what I have.
20170904_075800.jpg
 

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After looking at some diagrams it looks like I have a prestolite unit and its wired incorrectly. That jumper cable should be removed and a wire should be ran from the ignition posts to the ignition. The symptoms I'm getting are 8-9 volts on the battery gauge and 11.8 volts at the batteries. When the boat is idling the volt meter reads 9 volts. When its under way it reads 8 volts. Im guessing with that jumper cable the alternator is just putting out enough to get by. Is the reason the volts drop while under way is because the ignition is pulling more power than the alternator is putting out due to that jumper cable?
 

Dettom

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Dont know if you already solved this problem but, I had a guy in Havasu on Acoma rebuild my alternator a few weeks ago. Mine looks a great deal like yours and it was also wired incorrectly with that jumper wire like the one on yours. I discovered it wasn't a USCG approved alternator, unbeknownst to me. When he tested it it, it was barely putting out 60 volts. He rebuilt for me, did a one day turn-around, converted to a marine alternator. He did a great job and it was under 200 bucks. Can't remember the name of the shop but his name is Frank and he did a great job. The number is 928 706 8646.
 

racerden

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Been using the Summit G1667a (100A) for years. Good quality, chrome, won't break the bank. Best of all it's just a (1) wire hook-up (Large 12+V). It energizes with RPM over 1-1,200. Being in a V-drive race boat and semi-close to the bilge (water), when it gives up I don't bother rebuilding it, it gets replaced. Last I looked it ran around $100 or so.
 
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