69 Alternator Discharge
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69 Alternator Discharge
I am having issues with a 69 Corvette with a 427 and manual transmission. I have been having a continuing issue with my amp meter dropping to full discharge when anything on the lighting circuit is turned on. Driving down the road with no lights on, the amp meter shows charging, the needle at around +15v but the instant I switch on the running lights it drops to -15v. I have replaced the alternator which has internal regulator and no change. I am thinking I have a shorted wire in the lighting circuit somewhere. How do I troubleshoot where my problem is located?
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From: Sunshine Coast, Queensland, Australia
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Step one.
Go to Madelectricals Web site. Top of the home page about in the center, Tech pages. Click on tech pages.
Now, read everything on changing systems, the difference between one wire alternators and 3 wire alternators etc.
You will find these early charging systems expained so the average guy can understand.
Step two.
Before you condemn the car. Run a few tests. It's highly likely the issue is in that amp meter and not the charging system or the car.
Sooo, do you own a few basic electrical test tools?
At a minimum your going to need a voltmeter just to get started. These days you can purchase a test light with a volt gauge built-in. Damn there handy.
Get a volt gauge on that battery.
Basic tests.
Battery voltage with car off.
Battery voltage with car running at idle.
Battery voltage with car running at 2,000 RPM
Last 2 tests with headlights turned on.
Go to Madelectricals Web site. Top of the home page about in the center, Tech pages. Click on tech pages.
Now, read everything on changing systems, the difference between one wire alternators and 3 wire alternators etc.
You will find these early charging systems expained so the average guy can understand.
Step two.
Before you condemn the car. Run a few tests. It's highly likely the issue is in that amp meter and not the charging system or the car.
Sooo, do you own a few basic electrical test tools?
At a minimum your going to need a voltmeter just to get started. These days you can purchase a test light with a volt gauge built-in. Damn there handy.
Get a volt gauge on that battery.
Basic tests.
Battery voltage with car off.
Battery voltage with car running at idle.
Battery voltage with car running at 2,000 RPM
Last 2 tests with headlights turned on.
Race Director
Joined: Nov 2006
Posts: 13,068
Likes: 7,678
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Oh, and I've seen amp guages play up like that with loose battery cables.
Check both ends of all 3 cables, lots of people forget the third one. From engine block to frame on the passengers side. Years ago my third cable had gone green inside. I replaced that cable and my charging system improved immediately.
Check both ends of all 3 cables, lots of people forget the third one. From engine block to frame on the passengers side. Years ago my third cable had gone green inside. I replaced that cable and my charging system improved immediately.
Thread Starter
Instructor
Joined: Nov 2009
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I have a volt meter, I will make the tests you suggest, I also have an inductive amp meter, I will check to see if it's reading match the car's gauge. I will also check all the cable connections as suggested.
Race Director
Joined: Nov 2006
Posts: 13,068
Likes: 7,678
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
Sounds like a good start. If you turn on the lights and smoke comes out of the wires. Then yes I'd say you likely have a wiring problem. If the lights are working but that darn amp meter is acting strange. Keep testing.
report back with readings .
report back with readings .
