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Old 03-02-2010, 09:12 PM   #1 (permalink)
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Alternator overcharging

Hi,

I have a 69 Mustang with a 55A alternator and the ALT light is off at start, but stays on once the engine is running. The car has a new alternator, new (non-electronic) regulator, new battery, and new wiring.

I have replaced the new regulator once already with another non-electronic unit.

I pulled the alternator and had it tested and all is working correctly.

The multimeter shows 12.6V at idle and 16.9V as RPM's increase. Any idea what could be causing this? Are regulators bad from the factory? This is an NPD unit and their stuff has always been good.

Thanks,

Mike
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Old 03-02-2010, 09:16 PM   #2 (permalink)
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Re: Alternator overcharging

voltage reg. grounded ? internal & external .
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Old 03-03-2010, 09:32 AM   #3 (permalink)
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Re: Alternator overcharging

Yep, 16.9 V is about 2.5 V too high. For some reason your regulators aren't regulating. As mentioned, check for good grounds at the regulator mount, engine block and alternator mount.
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Old 03-03-2010, 10:19 AM   #4 (permalink)
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Re: Alternator overcharging

You are way too high. Are you sure the Regulator WIRING is GOOD and correct? There are directions somewhere to which wire does what. You need to drop that voltage at least 1.5 volts!
15.5 is the upper limit of what your car should experience in ANY situation.
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Old 03-03-2010, 10:56 AM   #5 (permalink)
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Re: Alternator overcharging

Don't drive it that way either. When I first got my classic mustang many many years ago, I took the cover off of my voltage regulator and saw it "sparking" so I tweaked it thinking sparking was bad. My voltage jumped to 17volts. My headlights were like those HID lights in new cars and I loved it. Until my battery exploded acid all over my engine bay.
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Old 03-03-2010, 11:11 AM   #6 (permalink)
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Re: Alternator overcharging

Battery Cables and Connectors - Fastronix Engine Ground Strap


Get a good engine ground strap like this one.
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Old 03-03-2010, 06:12 PM   #7 (permalink)
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Re: Alternator overcharging

Okay, I will re-check all ground when I put the Alternator back in tonite. The regulator that's on there is brand new, and it's the second one I've put on. Very strange.

BLOWN 68, you mention an upgraded ground strap. I have an upgraded stereo and two amps in the trunk. The wiring for the amps is 4 guage. The battery ground strap is a very stock looking one, probably about an 8 guage. Do you think this may be part of the problem?
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Old 03-04-2010, 07:37 AM   #8 (permalink)
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Re: Alternator overcharging

Mikeyd32,

It is always best to use heavy guage wire for a high draw system. I would put several heavy grounding straps tied to the frame. Here is a short article about running multiple grounds when using two high powered amps. Hope this helps. -Mike

How to Connect Multiple Ground Wires for a Car Stereo | eHow.com
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Old 03-04-2010, 12:22 PM   #9 (permalink)
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Re: Alternator overcharging

I would definitely try an electronic regulator first and once it's working go back to the crappy mechanical one. Mine completely screwed my charging system up and I went the electronic and never looked back.
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Old 03-04-2010, 03:16 PM   #10 (permalink)
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Re: Alternator overcharging

Ford service manuals at least on 60's generation cars usually have a segment with specs and directions on how to setup the regulator to basic specs. Then you make final adjustments to the reg to fine tune it.

17 volts is definetly too high. I have heard that the electronic type regs don't always perform properly. I would avoid those and stay with the normal type. Or add a 1 wire module to the alt and elominate the old regulator. Cleans things up and consolidates evreything into one assembly.

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Old 03-10-2010, 06:34 PM   #11 (permalink)
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Re: Alternator overcharging**UPDATE**

ALMOST THERE!! I put in a new regulator, and added a ground strap between the engine and the frame. The alternator is now charging high 13 or low 14 volts.

But the ALT light still is off when I turn the key to run, and then stays on while the engine is running. And to make matters even more weird, the light would go off when I turned on the head lights one night. Now however, the light stays on all the time.

Help....

Thanks,

Mike
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Old 03-11-2010, 12:58 AM   #12 (permalink)
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Re: Alternator overcharging

soounds like you still have a ground problem , body must be well grd. too
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Old 03-11-2010, 05:51 PM   #13 (permalink)
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Re: Alternator overcharging

Hi,

I'm not even remotely good at electrical stuff, so if I get what you're saying, I should ground the body to the frame? I thought since the car is a unibody they were one and the same... not true?

Thanks,
Mike
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Old 03-11-2010, 06:12 PM   #14 (permalink)
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Re: Alternator overcharging

You need to connect the body, usually at the fender apron/voltage regulator, to the battery (-) terminal and an even heavier ground connection from the battery(-) to the engine block.
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Old 03-11-2010, 08:26 PM   #15 (permalink)
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Re: Alternator overcharging

Mike, did the vehicle originally come with an alt light???
Has the dash cluster been changed or has a different wiring harness been installed??
You need a factory shop manual to check the wiring diagram & test each termination with a test light or meter.

Good luck on your witch hunt.

Has anyone installed a dual filiment light bulb in place of a single filment bulb or visa versa. That would cause feedback which would or could cause weird problems. Bill
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