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Old 03-20-2010, 03:53 PM
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Upgrading my alternator - what to do about cables & fusible links?

I've been having an electrical gremlin for a couple of years now.....batteries would just up and die. I've replaced them a couple of times, done all of the current draw checks with an ammeter, and still haven't found anything obvious.

So now, I'm thinking I might have a leaky diode in my alternator, so I'm going to go ahead and replace it. I have a 130A alternator now, and am wanting to go to 190A or 200A (the extra juice will help charge up the batts on my toyhauler when I'm towing it).

I've read that when I upgrade the alternator, I should also upgrade the cable from the alternator to battery #1, as well as from battery #1 to battery #2. This seems to make sense, but I'm wondering what to do with the two fusible links that are in the stock alternator to battery #1 cable? I don't want to just take them out as I might end up frying something down the road. Are the stock 12ga links OK with a larger alternator? Can I put larger links in (and if so, what size...10ga)? What about replacing them with a massive fuse? Anyone know what they're protecting (I'm guessing the battery if the alternator goes haywire and starts spitting out megavolts)?

Any suggestions?


Just did a couple more tests.....pulled the cable off the alternator and put an ammeter in line to see if there was any parasitic draw.....none, zip, nada. Put everything back together, started the truck and put my voltmeter across the battery posts in AC voltage mode to see if there's any leakage from the rectifier. I'm reading between 0.104VAC and 0.030VAC (it jumps around quite a bit). Does this sound like a leaky diode?

Last edited by littlejoe; 03-20-2010 at 05:43 PM. Reason: Clarification
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Old 03-22-2010, 05:23 AM
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Joe, replied to your PM. Please feel free to share that info if you'd like....
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