The Dodge Challenger Message Board

I just bought a 1970 T/A Challenger that is unrestored. After bringing it home and driving it a while I decided to start fixing some of the more obvious problems, one of which was while driving at night and coming to a stop all lights became very dim. The ammeter also showed a large deflection on the discharge side. Once back up to speed the lights became sufficiently bright once again. I replaced the battery, the alternator, and the voltage regulator. Now the problem is too much voltage. The headlights and panel lights are extremely bright and after a voltage check, the alternator is putting out 15 volts at idle and 18.8 volts at 2500 rpm. The ammeter needle is now fully pegged to the charge side. I returned the alternator and installed another new one, but still the problem existed. I returned the voltage regulator and installed a new one, but still the problem existed. To keep the alternator from ruining the electrical system I disconnected it from the voltage regulator but still the ammeter shows a full deflection to the right --- the needle is completely pegged on the charge side with a brand new battery. The only other thing I could think of was to order a brand new engine wiring harness from Year One. Well it got here today, I installed it, and you guessed it, I STILL HAVE THE SAME PROBLEM.
A friend suggested the alternator wiring may be reversed but thats not it either. I reversed the field wires and it showed just as great a needle deflection but on the discharge side. HELP!!!
THANKS IN ADVANCE..........RANDALL

Randall, I have the exact same problem with a 72 "A" body car. Did the same things, alternator, regulator, wiring harness, still boils the battery over charging. I found it odd that the field wire is hot with the key on even with the regulator disconnected and even more so that it shows ground with the key off. I think the problem is on the other side of the firewall and I am going to wait on that repair. I have installed an older model electo-mechanical regulator (69 Mopar) in the line of the field wire and it works just fine for now. It will stay this way until I break the car down for repair. If you find the problem, please post the answer. I'll do the same.

Off the top of my head this so shoot me if I am wrong.

Alternators put out more voltage than needed to charge a battery. The output is dependant on how fast it rotates and how much voltage is going into the field coil in the casing. The only problem you can really have is not enough voltage at idle so rule out the alternator.

The Voltage Regulator controls the amount of voltage going into the alternator and that controls the output.

I think I know what the problem will be but check you have it wired ok first.

It should not matter which way around the field wires are but usually the top one is getting battery voltage via the ignition switch and the lower pin of the regulator. The same source as the positive of the coil. Usually a blue wire. It must get its voltage from the battery side of the ballast resistor though so check that is right. You must have full battery voltage on this blue wire.

The other field wire (green?) goes to the top pin on the regulator.

NOW. The most important connection!

The casing of the regulator MUST have a good earth connection. So must the alternator via the engine.

This is where restorers always go wrong. All these nicely panted parts? Make sure there is no resistance between the casing of the alternator, the casing of the regulator, the engine, and the negative side of the battery. That should do it.

Also read my 'charging systems' piece somewhere in this section. Bear in mind the different charging rates for regular and low-maintenance batteries.

Hope I remembered this right and you get sorted.

I just looked it up in a 'trouble shooting guide' and in there it says under 'overcharging' to check the connections at the regulator are OK and then to take a wire and connect it between the negative battery terminal and the earth on the regulator which in our case (I think) is the metal body of the regulator. If doing that makes the problem go away then the regulator is not earthed correctly.

So basicaly it is saying what I was saying. Make sure all your earths are good. People tend to forget that the body and chassis of the car are 50% of the electrical circuit.

as Dave has said--check all grounds- from bat to frame and --battery to engine-this one is one I remember years ago causing a 70 roadrunner to burnout the battery

John Mac

Well thanks to all for the suggestions, but after checking and reconnecting all grounds the problem still exists. Dave, I even ran a ground wire from the negative side of the battery to the metal body and mounting screws of the regulator. I fired the car up, idled it, revved it to about 2800, watched the ammeter peg, and then cringed as my 8-track player went silent. Hopefully just a fuse. I am beginning to think the problem is "on the other side of the firewall" as Douglas said. I am at a loss and dont know what else to do. I think I will go lay in the back yard and look at the clouds...........RANDALL

By the book is the right way to do things and I wish in would identify the problem in this case. All grounds are good. You can go on business as usual (being willing to put off correct repairs) if you disconnect the present regulator and put an old regulator on in the field line, grounded of course. It works for me and our problems certainly seem the same (you have voltage to the field with the regulator disconnected). I think I lost a fuel gauge and brake lamps to this over charging. Any fix is better than destroying good working parts.

I will assume you measured the resistance between the alternator and the batt. neg. and it was almost nothing?

Lets think about this logically then.

I don't know how the regulator works but I guess it must act as a variable resistor in the green wire of the field circuit.

So if the voltage across the blue wire and earth is battery voltage or less the green wire has a low resistance to earth. That would give high current flow through the field coil and a high output.

As voltage on the blue wire increases the resistance in the green wire to earth must also increase within the regulator - limiting current flow through the field and reducing the output to the battery.

So (hopefully logically) for this to go wrong you must either;

a) Have a low voltage between the blue wire at the regulator and earth.

Or.

b) Have a short between the green wire at the alternator and earth.

What voltage have you got between the blue wire and earth?
Make sure you haven't got the ballast resistor wired the wrong way around. That would do it.
Also check there is no connection between the green field connector and earth when the regulator is disconnected.

I really am just making this up off the top of my head here but hopefully it will get you thinking at least.

Oh! And make sure you turn off any accessories while testing!!

Randlall's problem and mine may have different causes but the end result is the same. Both alternators are at full charge even with the regulator disconnected. In my case I have battery voltage at the blue wire, disconnected or not. Could this be the problem? The in line electro-mechanical regulator (blue wire)works well but the green wire terminal on the alternator must go to ground, just as on the older cars (69) which actually have only on terminal on the alternator. Thanks for the help Dave.

With the regulator disconnected you will have full output from the alternator. That is the point!! It is not in series with the field circuit. It is only the path of the green wire to earth that is controlled by the regulator. If there is output from the alternator with the regulator unplugged then the green wire side of the field circuit must be finding its way to earth someplace.

That's if I am right about how it works of course.

So the two checks to make are;

a) battery voltage at the blue wire with the ignition on but the engine not running.

b) open circuit between the disconnected green wire at the regulator and earth.

Dave said: With the regulator disconnected you will have full output from the alternator. That is the point!!

Sorry to disagree but you're wrong. With either wire or both wires disconncted you should have no output from the alternator. You should have battery voltage on the blue wire anytime the ignition is turned on. The blue wire runs from the ignition switch to both the control module and the alternator and serves three purposes. First it provides power to operate the control module. Second it provides power to the field coil in the alternator. Third, the control module monitors the battery voltage via the blue wire to determine when to activate the alternator. The green wire only connects between the control module and the alternator and it's only purpose is to control the alternator. Whenever the control module senses a low voltage condition it effectively grounds the green wire. That places a ground on the second side of the field coil in the altenator and energizes the feild coil. (Remember the other side of the field coil is connected to V+ via the blue wire anytime the ignition is turned on.) When the field coil energizes the alternator goes into a full outpout mode and stays that ways until the control module senses that the battery voltage is no longer low.

(Insert important point here: the output of all generators and alternators is controlled by their field coils. Apply power to the field coil, or in the case of Chrysler, complete the field coil circuit and the field coil generates a magnetic field. The interaction of the rotating magnetic field and the stationary coils in the alternator creates electricity. End of important point).

In practice the alternator is switched off and on very rapidly under most conditions. Under a light electrical load it's on for less time but under heavy electrical loads it's on for more time.

Note that this is completely different from the way that charging systmes operated when using electro-mechanical voltage regulators. In those sytems there was only one wire going to the alternator (not including the large wire that carries the power back to the battery) and the other side of the field coil was always grounded. In the electro-mechanical systems, the one wire supplied power to the alternator only when charging was needed. In the electronic system, power is supplied to the alternator all the time and the alternator is controlled by grounding the second (green) wire. The electro-mechanical systems also attempted to regulate the alternator output by limiting the voltage on the control wire. Most sytems only used one or two "steps" so regulation was crude. The electronic system doesn't attempt to regulate the alternator output. Instead It's either full on or full off. These systems switch it off and on rapidly to gernerate an AVERAGE voltage on the altenator output.

OK enough theory. Here's how to troubleshoot that problem. First make CERTAIN that both the control module, battery and alternator are well grounded. Unplug both wires from the control module. The alternator output should now go to zero even with the engine running. If it doesn't then there is a short (actually two) in the alternator (or the green wire is shorted to ground but that's not likely). Next short the green wire to ground. That should force the altenator to go into full charge mode. (Don't leave it that way more than a few minutes, it's rough on the battery). If that works then the alternator is almost certainly good. If it doesn't work then verify battery voltage on the blue wire at the alternator. If none then troubleshoot back to the ignition switch and battery. And check the fusible links carefully. They can cause some strange problems! In fact, in this case I'd say that they're the likely source of the problem.* If the battery voltage is good on the blue wire at both the alternator and control AND the alternator works manualy but not automaticly then replace the control module.

* A open or intermitant fusible link will cause the voltage in the electrical system to be lower than the actual battery voltage. The control module will sense that and believe that the battery is low and will therefore turn the alternator onto full output in an attempt to charge the battery. Since the problem is not due to a low battery, the charging circuit will continue to charge at full output until something gives! Carefully check the voltage on the blue wire against the battery voltage. If they're different by more than a couple of 1/10s of a volt then find out why.

PS I just thought of a quick way to check for this condition. Jumper the + side of the battery to the blue wire at the alternator or control module. (You can make this connection before or starting the engine as long as you can safely work around the moving fans, belts etc.) Start the engine. If the wiring is OK then no change in behavior will be observed. But if there is an open fusible link or other wiring problem then this will bypass it and charging should return to normal. Just to be safe, I'd put a 5 or 10 amp fuse in that jumper wire. Otherwise if there's a short in the wiring you could damage something. FWIW I've never seen a problem with the fusible links in Chryslers but I have seen it in other cars and it can cause some real strange behavior.

That should find 99+% of all the charging problems. Let me know if you need more help.

At last!

We have an Auto Electrician on the board! Hurray!

Glad to see you Joe. I have been struggling with electrical questions on here for years. It is a load of my mind if you can look out for these ones for me.

You took that statement of mine out of context there Joe. Plus I did not pick my words very carefully! If you read the rest of that post AND the one before it you may be able to see that what I was trying to say was that with the regulator disconnected AND a short to earth from the green wire side of the alternator (the suspected fault) you WILL STILL get full output from the regulator EVEN WITH THE REGULATOR DISCONNECTED.

My fault for not being very clear.
Anyway. Good to have you on board. Cheers!

Hi Dave,

Sorry for the confusion. I was in a hurry reading through all messages and I undoubtly missed parts of them. You are quite correct about being able to get full output from the alternator even with control module disconnected. That's one of the things that I like about the Chrysler system, it makes it very easy to troubleshoot. AND it's handy in case of a module failure. I was discharged from the USAF in Vermont and was driving my '70 Duster back to Virginia when mine failed but I was able to keep going by grounding the green wire for an hour then leaving it off till the battery got low and then repeating the process over and over till I got to where I was going (1200+ miles).

Yes, I think I can help you with any electrical questions. I have 30 years experience with Chryslers, almost 40 years experience in electronics repair, a degree in elctronics and another in computer science so I hope I'm qualified.

A damn sight more qualified than me mate! It was my Challenger that started me off. When I bought it in 1989 none of the electrics were working correctly. I knew absolutely NOTHING about auto electrics. It was a complete mystery to me.
So I read a book and got stuck in! Fixed the Challengers problems myself. After that I realised that there was probably nothing on these cars that I couldn't learn to fix. They are so simple. I wouldn't like to mess with newer cars though!

Dave, they say experience is the best teacher

I used to think that the Challengers were complex (when compared to the 1960s cars). But they're nothing compared to today's cars. I recently had to work on one of the interior air vents in my wife's 2000 Mitsubishi Diamonte. The dammed thing uses a stepper motor to open and close it and has it's own microprocessor!