Forget the blue wire. The automatic shutdown, (ASD) relay turns on for one second when the ignition switch is turned on, then again during engine rotation, (cranking or running). That relay feeds the ignition coil, injectors, fuel pump or pump relay, oxygen sensor heaters, and the alternator field winding. That's the blue wire. It will always have full battery voltage on it when that relay is on. That blue wire goes one more place, that is back to the Engine Computer, but it has nothing to do with the charging system there. The computer thinks it turned the ASD relay on. 12 volts on that wire simply verifies that occurred.
As a side note, when you have a crank / no-start condition on any Chrysler product, and don't know where to start, check for 12 volts on that blue wire during cranking. On later models that is almost always a dark green / orange wire. It will be the wire that is the same color at every injector, as well as the ignition coil pack and alternator. If you see 12 volts for one second when you turn on the ignition switch, the ASD relay and its circuit are working. What's important is if that voltage comes back during cranking. When it does not, the crankshaft position sensor and the camshaft position sensor are the two best suspects. Their signals are what tells the Engine Computer the engine is rotating. Those sensors commonly do not set diagnostic fault codes right away, so don't let the absence of a related fault code fool you.
The engine runs, so we know the ASD relay is turning on, and voltage is feeding the alternator's field winding. If it was missing due to a corroded splice in that blue circuit, you'd have a no-charge condition. To have such a serious over-charge condition, either the green wire going to the voltage regulator is grounded, as I suspected, the voltage regulator circuit is shorted inside the computer, which I'll admit is a possibility, or the system voltage sensing circuit has a break in it. The sensing circuit is usually also the feed circuit for other systems, so when that has a problem, there's usually other symptoms in addition to the over-charging.
I had a lot of "bugs" built into donated cars for my students to diagnose. Chrysler was very good to my school. Their instructors would drive a vehicle for a few months, and they'd be poked and prodded by their students, so they didn't want to sell them to the public. We had a '97 Dakota, quite a few Shadows, and a '95 Intrepid. Some of my bugs that could be switched in were that green wire was grounded in multiple places. Each one could be narrowed down by disconnecting plugs to isolate different parts of the circuits from each other. I did have bugs built into Engine Computers too, and those included a defective voltage regulator. Even that couldn't pull the green wire down to much less than four volts.
If you are right about the regulator being shorted, a replacement computer will solve the problem. If my best guess is right, that green wire has to be grounded somewhere.
Adding an external voltage regulator that you mentioned is a way around this problem if the one in the computer is shorted, but it comes with a whole new set of problems. The obvious one is when it's built into the computer, it can turn the alternator off completely during wide-open-throttle when you might need that extra five to ten horsepower. It can reduce alternator output when the engine is running hot, to reduce load, and it can anticipate the switching on of the AC compressor to eliminate the momentary dimming of head lights, dash lights, and slowing of the wipers and heater fan, by bumping up output a fraction of a second before it switches the compressor relay on. Those features are lost with the use of the external regulator.
The bigger problem is the Engine Computer watches the field current going through the regulator circuit. That actually pulses on fully, to around three amps, then off fully, to 0.0 amps, about 400 times per second. The ratio of on-time to off-time is varied to adjust the average field current according to the needs of the electrical system. When you cut the green wire to run it to the external regulator, that leaves the computer's circuit open, and there's no field current to switch on and off. That lack of current will be detected, and it will set a diagnostic fault code for "Field circuit not switching properly".
Two problems result from this fault code. First, the fuel injectors will not open at the right time or will not stay open long enough when supply voltage is wrong. That can result in increased emissions. Any fault code that is related to something that could adversely affect emissions must turn on the Check Engine light. The "field circuit not switching properly" code is one of them that turns the light on. Once that occurs, how will you ever know if a second, unrelated fault code sets? That second code could result in an expensive repair, such as a melted catalytic converter. You'd never know that second problem developed.
The other problem is for any fault code to set, there is always a long list of conditions that must be met, and one of those is that certain other codes can't already be set. As an example, with low system voltage, computers do weird things, and they read sensors incorrectly. You could develop a problem related to just one injector circuit, but the computer has stopped running tests on that circuit because it knows the results can't be trusted since a code is set for the charging system. A problem could develop, but with the tests suspended, you'd never know it. This happens a lot with engine performance problems and there's no related fault code to tell you where to start looking.
You might have to experiment with adding about a five to six ohm resistor between the blue wire and the green wire that goes to the computer, after you cut it off. That would give the voltage regulator a small current to switch on and off, and that might prevent the computer from detecting a problem, setting a fault code, and turning on the Check Engine light. Chrysler's old external voltage regulators from the '70s will run this alternator just fine, but I never tried using a resistor to trick the computer.
Friday, March 29th, 2019 AT 7:46 PM