1972 Dart 225ci Auto
I have had it. For the last 4 weeks, I have been unable to figure out why my alternator is putting out up to 18-20 volts. I have replaced the alternator 3 times, voltage regulator 2 times, battery, battery cables, and alternator wires. Gave up and took it to a mechanic. He said he found some melted wires behind the dash, replaced them and the problem was fixed. Paid him $230, drove it home and the next day it was doing the same thing. I got energized and started looking again. Then I just knew I'd found the problem......The #12 wires running from the dash amp meter to the big multiwire connector at the firewall were melted. I removed the dash and separated the melted wires, cut them out and installed new temporary wires to see if this remedied the problem. It didn't. Then, after the engine ran for a little while, it died and won't start. I have never been this frustrated. Anybody who has any ideas, I'd love to hear them. Thanks much.....Gary

If this is a dual field alternator, check the wires running from the VR to the alternator. One wire runs between the alt and VR only (this wire may or may not be green...) If this wire is grounding out, it will full-field the alt at all times (max alt output)

Also, where are you measuring your voltage? Measure it at both the alt output terminal and at the battery. If there is a significant difference bewteen the two (more than 1 volt difference) your charge circuit has too much resistance somewhere, most likely at the ammeter.

Have you tried bypassing the ammeter to see if the problem persists?

-S/6

God bless you. You seem to know your business. Please stick with me. Let me describe my alternator......One big power wire, one blue wire connecting to the "field" spade terminal, and one green wire connected to a "ground" terminal. The ground terminal on the alt is a spring loaded brush which rides on the armature (i guess). Now...both small wires go to the VR. Yes, I have bypassed the alt and no luck. I am measuring voltage at the battery. I have not measured the alt output. Please tell me what to do. Thanks so much

The alternator grounds through its case/bracketry. DO NOT run the engine anymore with the charging system the way it is---it may start a fire

It is putting out 18-20 volts because the green wire is grounded. The green wire should run to a second field terminal on the alternator...right next to the field wire the blue wire is hooked up to. (which wire hooks up to which field terminal on the alt does not matter)

The VR controls alternator output by intermittently grounding the green field wire through its case (there is more to it, but that is the funtion of the green field wire). With the green wire on the ground stud of the alt, the VR is 'telling' the alternator to full-field (charge full blast) at all times.

Hook the green wire to the second field terminal on the alt and your charging system should function normally.

If your alternator does not have a second field terminal, you have either the wrong alternator or the wrong voltage regulator. I am unsure what year the charging system changed from single to dual field alternators....

-S/6

Why the heck didn't he know that? He has been in this business for years. I don't understand how this car has been running so long wired this way. But it definately explains the melted wires that I spent all day laying on my back on the floorboard replacing. I have no second field terminal on the alt. Is there any way to wire it with the existing alt or should I return? The auto store said this was the alt made for this car???? Thanks again

Here is info on both single and dual field mopar charging systems. Looks like everything '70 and up had dual field charging systems, so it sounds like you have the wrong alternator (or the second field terminal has broken off)

Here is a wiring diagram for a Mopar dual-field charging system.

Hope the above info helps. IMO the parts store gave you a wrong, damaged, or mis-packaged alternator.

-S/6

_________________
The "Silver Bullet"
87 Ram D150

I'll post results after I exchange the alt. I really appreciate your help....Gary

I'll know if the new alternator fixes the problem (see "no fire from distributor" Thanks

Remember, the voltage regulator requires a good ground to the body of the car. A poor ground can cause high voltage like you are having.

For the archives.......Sorry for the delay, thanks to Hurricane Ivan.....Had to pull the wiring harness out of the dash and replace several melted wires. Got it all put back and exchanged the alternator for a dual field alt. This corrected the problem. The auto parts store's computer called for a single field alternator.....One spade terminal. THIS IS NOT CORRECT!!! The alternator he gave me, according to their computer, was for a 79 Barracuda or something. But it had two spade terminals and that was what I needed. Many Many thanks to Super6 and everyone else who helped.