Alternator charging issue. -
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post #1 of 3 Old 03-11-2006, 02:36 PM Thread Starter
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Alternator charging issue.

Ok, I've had a charging problem for some time now. Basically the alternator just barely puts out any juice, like 12v at idle, and less if lots of accessories are on. First off I had the alternator rebuilt. I see the guy test it on the machine in the shop before he gave it to me, so I know it was putting out 14.5V at 60A when he gave it to me. I plop it in, and the same problem persists.

As a temporary measure, I tried tying both the "remote voltage sensing" terminal (originally had the red wire from the connector), and the ignition source terminal (originally had the brown wire from the connector) to battery voltage. Low and behold, the alternator starts churning away and I get 14.4V across the battery. I then tried keeping the regular voltage sense wire intact, and placing 12v onto the ignition source terminal. Same deal, charges great. By now I figure there is a problem with the wiring coming from the ignition.

I disconnect the main wire harness plug from the firewall (by the brake booster) and found where the ignition wire ran from inside the cabin to under the hood. I checked the resistance between here and the brown wire on the alternator connector and found it to be 15 ohms. I know there is a resistor/resistance wire in line along the way, so this value should be correct.

I even read 12V on this line when the ignition is on, so I know it is working properly. If I run a straight wire from the ignition source to the alternator, it works fine again as if I had attached it to 12V (but I can't turn the jeep off this is what the resistor on this line prevents; feedback voltage). I then try using a 10 ohm 10W resistor with the jumper wire and no charging.

There HAS to be a problem with the alternator even though it was just rebuilt, right? I'm about ready to pull out my hair, because there is nothing left to go wrong, I've tested it all I beleive.

Someone must be knowledgable enough about a YJ's wiring/charging setup to help me out. Any advice at all is GREATLY appreciated.


Last edited by Bobbywolf; 03-11-2006 at 02:55 PM.
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post #2 of 3 Old 03-12-2006, 10:46 AM
Jerry Bransford
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I think you have mixed up the alternator's sense wire with the resistor wire that provides power to the ignition coil once the engine is started. The ignition coil uses a resistor wire for reduced voltage once the engine has started (and another non-resistor wire for starting) so when you jumped that wire, that's why the engine wouldn't stop when you turned the ignition off. The alternator does not use a resistor wire for its sense lead to the best of my knowledge.

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post #3 of 3 Old 03-12-2006, 12:10 PM Thread Starter
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I didn't mean that the remote voltage sensing had a resistance wire, but the one running from your ignition switch does, all vehicles have to if you don't have an indicator light. The light, or the resistor are what stops the back voltage from keeping the jeep running after turning the key off.

I read up a fair bit about this, and I'm now convinced 90% that my rebuilt alt is to blame.
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