Battery drain

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Oct 26, 2025 | 01:04 PM

kevdog442

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Joined: Jan 2008

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From: Zanesville, Ohio

Battery drain

69 Cutlass, trying to figure out a battery drain issue. Drains overnight. With the battery negative disconnected I have full voltage from that post to the engine ground. I hooked up a test light and pulled each fuse. The light never went out. This has an external regulated alternator which is charging fine. Recently replaced the regulator but it didn’t fix the problem. Thinking maybe just old wiring?

Oct 26, 2025 | 01:16 PM

matt69olds

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Joined: Jan 2010

Posts: 6,105

From: central Indiana

Disconnect the heavy red wire from the back of the alternator and test again. You may have a leaky diode.

Oct 26, 2025 | 01:18 PM

Fun71

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Posts: 15,409

From: Phoenix, AZ

Unplug the harness on the alternator. There could be a bad (leaky) diode.

Oct 26, 2025 | 02:33 PM

illumined

1978 Ninety Eight

Joined: Jul 2014

Posts: 463

There could also be a short, do all your electrical work fine?

Oct 26, 2025 | 02:40 PM

kevdog442

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Joined: Jan 2008

Posts: 469

From: Zanesville, Ohio

Quote:

Originally Posted by matt69olds

Disconnect the heavy red wire from the back of the alternator and test again. You may have a leaky diode.

The test light goes out when I unhook either one of the connections at the alternator

Oct 26, 2025 | 02:41 PM

kevdog442

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Joined: Jan 2008

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From: Zanesville, Ohio

Quote:

Originally Posted by illumined

There could also be a short, do all your electrical work fine?

yes

Oct 26, 2025 | 02:56 PM

Fun71

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Joined: Feb 2013

Posts: 15,409

From: Phoenix, AZ

Quote:

Originally Posted by kevdog442

The test light goes out when I unhook either one of the connections at the alternator

Sounds like you found the problem. If you want 100% confirmation, you can bring the alternator to an auto parts store and have it tested.

Oct 26, 2025 | 03:48 PM

kevdog442

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From: Zanesville, Ohio

Alternator tested fine, diode ok. Gonna go through the wiring connections

Oct 26, 2025 | 04:22 PM

Sugar Bear

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How/wherer was the alternator tested?

Oct 26, 2025 | 04:42 PM

#10

kevdog442

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Joined: Jan 2008

Posts: 469

From: Zanesville, Ohio

Quote:

Originally Posted by Sugar Bear

How/wherer was the alternator tested?

I had the car running with lights on, disconnected the positive. Stays running. For the diode I went to the school of YouTube and watched a few videos. Tested with a multimeter.