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Old 03-08-2012, 05:26 PM   #1
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voltage regulator

Ok, first it was "kinda working", by that i mean that the battery (new) wasn't fully charging, and the alternator tested good. So, everything seemed to point to the voltage regulator..., but don't these either work or not? Anyways now it doesn't want to regulate at all period. I even got a couple of good used ones from a friend that didn't work either. My question is does the regulator (on the firewall....this is a old 72' truck) need to have a good ground? Someone told me they had a similiar problem that they finally resolved by running a small ground strap from the one of the bolts attaching the VG to the firewall, to the engine block. Haven't tried this yet, ran out of daylite before I could find a suitable ground strap to use.
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Old 03-08-2012, 05:53 PM   #2
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Yes, must have a good ground to operate properly.
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Old 03-09-2012, 07:40 AM   #3
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Here is a simplified diagram from "MyMopar:"


In the diagram below, notice the wire from the IGN switch to the coil ballast, and then off towards the regulator. Notice that a blue and a blue/ white "Y" off to both the regulator and one of the alternator field connections

Turn the key to "run", engine off, and take your meter and probe the blue at the althernator field WHILE IT IS still hooked up.

Stick your other probe on the battery POSITIVE post, set to "low DC volts". You are looking for a VERY low reading, the lower the better. You are measuring the "voltage drop" through the harness from the battery, through the bulkhead connector, through the IGN switch, back out the bulkhead connector, and to the alternator/ regulator.

You DO NOT want to see much over .2V (two TENTHS of a volt.) Much over this, you have a bad connection in the cricuit path mentioned above. Over .5 (1/2 volt) means you REALLY need to look things over. This drop will cause poor regulation as well as over charging.

Next, take a critical look at the regulator CONNECTOR. Is it loose? dirty? corroded? The connections MAY be broken inside the molded connector. You can buy these, last I looked, at NAPA. Work the connector in/ out of the regulator connector to "scrub" the terminals clean, and make sure it fits tight.

Read this article from MAD electric:


which came from here:


Look over the simplified diagram on the page. At LEAST two points in the diagram that are chronic trouble on Mopars is the BULKHEAD CONNECTOR. In particular are the connections for the battery feed and the alternator charging line.

Fire up the engine and run at a fast idle. Check the battery voltage, what is it?

Should be close to 13.8-14.2, in no case below 13.5 and in no case above 15

IF the battery voltage is low, move your meter over to the output stud on the alternator. IF there is more than about 1 volt difference, you have harness/ bulkhead connector/ ammeter circuit problems.

Other problem areas in the bulkhead connector is the blue "ignition run" circuit, and the headlights.
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Old 03-10-2012, 05:01 AM   #4
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Got any suggestions on why one would bounce from full charge to center? It's so bad my headlights look like a cop is trying to pull you over with white flashing lights. New regulator, new alternator.
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Old 03-10-2012, 08:52 AM   #5
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Sounds like a bad connection or bad brushes.

Go through step by step what I posted

Read the MAD article

Wiggle wiring. "Rig" a voltmeter so you can see it, get the engine on a fast idle, and if necessary, turn on the headlights if that "helps" the problem to show up. Wiggle the regulator connector, the field connectors at the alternator, and move the wiring around immediately close to the bulkhead connector.

This could be a LOT of things

Problem in the alternator

Bad connection/ connector at the regulator

Bad connection/ broken wire from regulator IGN terminal to ballast resistor junction

Bad connection in IGN "run" supply circuit, to check this, disconnect BLUE wire at alternator field SO IT DOES NOT CHARGE, and "rig" voltmeter to the blue wire. Look for up/ down voltage fluctuations at the blue wire, which is hooked to IGN "run" buss.

Bad charging line wiring (follow the simplified diagram on the MAD page) all the way from alternator stud -- at bulkhead -- through ammeter circuit -- bad "in harness splice" -- bad ammeter (check for melted plastic in dash, and wiggle wiring at ammeter, AND check for heating at ammeter) -- BACK out through bulkhead connector -- to battery
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Old 06-09-2012, 07:47 AM   #6
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i had this trouble on my 84 ram... i took off the vr sanded the firewall with sand paper and re mounted it.. that fixed it for me.. sometimes the simple thins work best
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Old 06-09-2012, 04:32 PM   #7
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michuy -

If you know every thing is grounded properly and you changed the regulator, replace or rebuild the alternator.

Been there, done that. Yes, even if the alternator checks out fine with volt / amp meters.

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