Hi guys. Please allow me to add a few comments of value. Chrysler was the first manufacturer to use an electronic voltage regulator in 1970 models, and it can be a dandy part to run other alternators. One problem here is the Engine Computer monitors current flow through the field winding and its internal voltage regulator circuitry. When the internal regulator is bypassed, the computer sees 0 field current. It will set a fault code for "field not switching properly", and since low system voltage could adversely affect emissions, that code turns on the Check Engine light. That in itself doesn't cause a problem. The concern now is if some other, totally unrelated problem develops and sets a different fault code, the Check Engine light is already on, so you'll never know that new problem has developed. That new one could be a very minor one that turns into an expensive repair if it is unwittingly ignored.
If you want to keep the external regulator, I would connect a resistor between the switched 12-volt feed, to the terminal at the computer where the wire went to the alternator. Field windings are very close to 4 ohms, so use something close to a 4 ohm to 6 or 8 ohm resistor. This will have to be at least a 20 watt resistor. Those are ceramic, usually about 1/2" square by a good inch to an inch and a half long. They were commonly used on older tvs with picture tubes.
As for testing the charging system, let me start with the older Chrysler systems from the 1970s, the era your regulator came from. There's two wires connecting the regulator and alternator. The dark blue, along with all the other dark blue wires under the hood, has 12 volts on it when the ignition switch is turned on. That supplies the field current for the alternator, it powers the regulator circuitry, and it is the wire the regulator senses system voltage on. The regulator needs a reference when it measures system voltage. That "reference" is a fancy way of saying it compares it to ground. In this case, that is the regulator's metal housing. It has to be bolted to a paint and rust-free point on the engine or body sheet metal.
After current flows through the alternator's field coil, it leaves on the green wire and goes to and through the regulator's circuitry, to ground, so again, you need that good ground on the regulator. The regulator changes its internal resistance according to changes in system voltage, to adjust how much current flows through the alternator's field coil. Adjusting field current adjusts the strength of the electromagnetic field, thereby adjusting how much voltage is developed in the stationary "stator" coils. That adjusts how much current is developed, which is always just as much as is necessary to meet the demands of the entire electrical system, and to recharge the battery.
To test a system that appears to be dead, watch the brightness of the headlights, or place a voltmeter across the battery terminals, then ground the green wire. Doing so will bypass the voltage regulator and run the alternator wide open. Do not raise engine speed during this test. All generators are relatively inefficient at lower speeds. That is what can save you from destroying multiple computers and burning out any bulbs that are turned on. The battery is also helping to hold system voltage to a safe level, so never, ever disconnect it with the engine running. A good alternator that is full-fielded, with raised engine speed, can easily develop over 30 volts. With the battery connected, it helps hold that down to around 18 volts.
During this "full-field" test, expect to see battery voltage rise to around 15 to as much as 18 volts. Do that just long enough to get the reading. If you see that rise in voltage, the alternator is working although it can still have a problem with one failed diode of the six. That's a story for later. If you do not see a change in voltage, check to see if there's 12 volts on the dark blue wire.
For your newer model, testing is done exactly the same way, but there's a new wrinkle you'll have to contend with. That is, . . . the two wires, (dark blue and green on the older systems), go through a black, plastic block bolted to the back of the alternator, then pop out as the two metal tabs bolted to the small terminals on the alternator. There's no easy way to know which tab goes to which wire. If you guess, and you guess wrong, and ground the 12-volt feed wire, you'll blow the fuse feeding the automatic shutdown, (ASD) relay. That relay also feeds 12 volts to the injectors and ignition coil(s), so the engine will stall.
There are ways to figure out which terminal to ground to full-field the system. When the charging system is working, one terminal will have full system voltage, the other will have considerably less, typically 4 to 11 volts. That's the one, with less voltage, to ground. The lower that voltage is, the harder the regulator is driving the alternator.
The problem is when the system is not working, and you find exactly the same voltage on both field terminals. That happens when there is no field current flow, typically due to a break in the control wire going to the voltage regulator. That break can be caused by a defective regulator circuit inside the Engine Computer, but it's much more common to find corroded terminals in the connector in the middle of that harness where it goes from engine to body. You can't use a voltmeter to determine which wire to ground. They operate without drawing current from the circuit, so there's no "voltage drop" across the field. You'll see the same voltage at both points.
Some people will figure out that an old-fashioned incandescent bulb test light DOES draw current to do its thing, so it will cause a small voltage drop to occur, then the voltage on the control wire will be lower. The problem is you have to physically remove the test light's probe from one terminal to move it to the other one. You'll never see on which terminal the light is brighter.
The secret is to use both the test light and the digital voltmeter at the same time. On one terminal the light will be full brightness and the meter will read full system voltage. On the other terminal the test light will still appear to be full brightness, but the voltage will be lower, if only by a few tenths of a volt.
Now that you know which terminal to ground, do the full-field test and see what happens to battery / system voltage. If it doesn't go up a lot, measure instead right on the fat, bolted-on alternator output wire. If voltage rises there, there has to be a break in the wire going back to the battery. On vehicles as new as yours, there is usually a large fuse bolted into the under-hood fuse box that is just for this circuit. It could have been blown by your original alternator if it had two shorted diodes. Older models used fuse link wires. Those are short sections of special wire spliced in that are of a smaller diameter, making them the weak link in the chain. The insulation is designed to not melt or burn. This one will be very close to the battery. You test them by tugging gently on them. If one is burned open, it will act like a rubber band. If it's good, it will act like a wire.
The important point is you can't just check if there's voltage on the three alternator wires. You have to look at the exact voltages and compare them to determine what is or isn't working. If I've left you more confused than before, measure those voltages as precisely as you can, with the engine running, then post them in your next reply. MECHTRIX will help you figure out where to go next. I'll be sitting on the side waiting to learn the solution.
By the way, for your next trivia contest, Chrysler was the first manufacturer to develop the "AC generator" for their 1960 models, and they copyrighted the term, "alternator". GM didn't have their version until 1964.
Sep 21, 2026 at 5:32 PM
