Hi guys. There's one more thing to consider. The external voltage regulator from a 1970 through late '80s Chrysler will run this alternator just fine, but the resulting lack of field current flow through the Engine Computer's voltage regulator circuit will be detected, and the diagnostic fault code, "field circuit not switching properly" will set. Since that normally refers to a failure-to-charge and therefore low system voltage, that can adversely affect injector response and ignition spark strength. Those two things could adversely affect emissions, therefore, that fault code turns on the Check Engine light.
Once the Check Engine light turns on, some of the hundreds of tests the computer continually runs will be suspended. That is when a second, or third, totally unrelated problem could develop, along with a variety of symptoms, but not be detected by the computer. No one, especially the mechanics, would find any new fault codes or have that information to direct them to the circuit or system that needs further diagnosis. You would have to fix the first problem the proper way, with a replacement computer, erase that fault code, then drive the vehicle until the newer problems are detected.
This is where you'll hear stories about someone getting their vehicle repaired, they leave the parking lot, and within a fraction of a minute to a few miles the Check Engine light turns right back on again. The owner incorrectly assumes the vehicle wasn't repaired correctly or wasn't diagnosed correctly. The mechanic is frustrated because he had no way of knowing once the first repair was completed, and the suspended tests resume, that the newer problem will now be detected, and the light may turn on again. This is more likely to happen when a lot of time passes, as in many months, before the first problem is addressed. That gives all that time for the new problem to develop.
In addition, even if a new, second or third problem develops, you would never know because the Check Engine light is already on, so it gets ignored. That can result in a fairly simple or inexpensive problem turning into a very expensive repair.
If you want to pursue this for a temporary fix, use the simple diagram below. You will likely have a little silver Nippendenso alternator as shown in the first photo. There's two small terminals on the rear. They're interchangeable. My sad drawing shows the three-terminal plug that has just two wires in it, a dark blue one and a dark green one, for the regulator. Those two wires go to the two terminals on the back of the alternator. Then, the dark blue wire gets tied to anything under the hood that gets 12 volts switched on. On the older models, everything dark blue under the hood got 12 volts switched onto it through the ignition switch when it was turned to "run". On newer models like your truck, the field current is switched on through the automatic shutdown, (ASD) relay. You can get that 12 volts from the positive terminal on one of the ignition coil, or the 12-volt feed wire at any of the injectors. The third diagram shows the ASD relay switching 12 volts onto the dark green / orange wire at all of those places. That's the most often used color now instead of dark blue. The fourth diagram shows the same wire / circuit at two of the ignition coils and two of the injectors. All six of the others are exactly the same, so you can use that wire at any of them.
I don't consider this a proper repair or anything other than a temporary fix, but it can get you back on the road again. These regulators were very inexpensive, as in usually under $20.00. They also have a third terminal that must be used. That is the metal housing bolted to the body sheet metal for the ground. Be sure paint and rust don't interfere with that connection.
(In the second drawing, top right, where it says, "to ignition switch", for your truck it should say, "to ASD relay circuit", or "to dark green / orange wire).
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Tuesday, November 22nd, 2022 AT 7:23 PM
