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86-95 Trucks & 4Runners 2nd/3rd gen pickups, and 1st/2nd gen 4Runners with IFS

Overcharging issue

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Old Aug 26, 2024 | 10:05 AM
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Camoray88's Avatar
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From: Alabama
Overcharging issue

Few days ago I noticed the battery light and e-light come on the dash while piddling around the yard. Checked everything out and noticed the main lead going from my battery to fuse block under the hook was hot. With a quick voltage check I’m getting 18v while running to the battery (obviously not good). Any ideas on what could cause this?
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Old Aug 26, 2024 | 10:44 AM
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Voltage regulator in the alternator is bad. Had this happen to me and it cooked the main power wire and never blew any fuses
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Old Aug 26, 2024 | 10:50 AM
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The White wire (Sense) on the 3 terminal connector to the alternator should be at battery voltage key-on or key-off. If that wire opens, the regulator will keep fruitlessly raising the voltage to get the sense voltage to come up.

So the first thing I'd do is back probe the white wire and check voltage to ground (and wiggle the wire to be sure).

If you have battery voltage at the white wire, my next guess is a failed regulator. Unexplainably, the regulator alone is about twice the price of the whole alternator at RockAuto. So before I bought anything, I'd take the alternator to a local parts store to have it tested (usually free). Get the price of a replacement alternator first; the whole reason they do [free] testing is so you'll buy your replacement right there. Then you'll know how much you can pay for the one-stop convenience.
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Old Aug 26, 2024 | 01:12 PM
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Appreciate the info man, chased down that white wire and sure enough it had a break it in. Voltage is back down
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Old Aug 26, 2024 | 07:25 PM
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Thanks for the report. Glad you could fix it.
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Old Sep 9, 2024 | 12:01 AM
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Originally Posted by scope103
The White wire (Sense) on the 3 terminal connector to the alternator should be at battery voltage key-on or key-off. If that wire opens, the regulator will keep fruitlessly raising the voltage to get the sense voltage to come up.

So the first thing I'd do is back probe the white wire and check voltage to ground (and wiggle the wire to be sure).
Spoiler
 
If you have battery voltage at the white wire, my next guess is a failed regulator. Unexplainably, the regulator alone is about twice the price of the whole alternator at RockAuto. So before I bought anything, I'd take the alternator to a local parts store to have it tested (usually free). Get the price of a replacement alternator first; the whole reason they do [free] testing is so you'll buy your replacement right there. Then you'll know how much you can pay for the one-stop convenience.
Thanks for sharing it, you made my day.

Last edited by FrederickJunkins; Sep 20, 2024 at 11:48 PM.
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