Hi guys. Excuse me for butting in. Let me add a little. The Engine Computer will detect it when there is no field current through the regulator circuit and will set a fault code for "Field circuit not switching properly". I can't remember for sure but I think that will cause the Check Engine light to turn on. The light turns on for any stored code that can have an adverse affect on tail pipe emissions, and low system voltage can do that due to weak spark and low voltage to the injectors. If the light is on, you will never know if / when a different problem is detected because the light will already be on.
The voltage regulators inside Chrysler Engine Computers give extremely little trouble. To verify it is really defective, find the dark green wire in the 60-pin connector, pin 20. It is at the very end of the top row of pins, toward the rear of the car. Grounding that wire while the engine is running should full-field the alternator. Lights will get bright and system voltage will go up. Don't increase engine speed during this test as the excessive voltage will take out bulbs and computers. If there is no change in voltage, the regulator isn't the problem. The most common cause of failure to charge, especially intermittently, is worn brushes in the alternator. They can be replaced without removing the alternator from the engine if you have the silver Nippendenso unit. I did that many times to "bug" cars for my students to practice troubleshooting skills.
The regulator Wrenchtech mentioned was used from 1970 through 1983 on all Chryslers and up through 1989 on the Fifth Avenue. It has temperature compensation built in to bump up the charging voltage a little in cold weather since charging a battery is a chemical reaction, and they don't work as efficiently at colder temperatures. I just did this same modification to my New Holland skid steer and it works better than the original regulator that was built into the generator.
This regulator actually has three connections. The third one is the case which has to be bolted to the body sheet metal or engine. That is its ground. The electrical connector is a triangle with two pins and a space where the third pin would be. The diagram Wrenchtech found is for the '69 and older cars with a mechanical regulator. It will work with your alternator too but is harder to wire in and a lot harder to find.
Before you start snipping wires, check for battery voltage on the two small terminals on the back of the alternator. One should have full battery voltage and the other one should have less, typically 7-11 volts, but never 0 volts. Those voltages will only be there when the engine is running, not just with the ignition switch turned on. If both have exactly the same voltage, the regulator could be open, but more commonly the dark green wire going to it has a bad connection. That's where grounding that wire at the Engine Computer will prove the wire is ok. If you find 0 volts on just the second terminal, the brushes are worn. Modifying the circuit won't help with that.
The two small wires on the alternator are dark green and dark green with an orange stripe. The problem is both go into a black plastic block so you can't tell which wire goes to which terminal. When the system is working properly, the terminal with the slightly lower voltage is the one without the stripe. If the regulator or wire are open, you'll measure the same voltage on both terminals. To tell them apart you would have to unbolt the block so you can measure which one has voltage, (dark green / orange), but you risk twisting the tiny studs off. I can share a trick to figure out which is which if you run into that problem but it will require a test light AND an inexpensive digital voltmeter.
Remember, these voltages only appear when the engine is running because they come from the automatic shutdown relay which is turned on whenever the Engine Computer sees engine rotation. To connect the old style electronic regulator, the terminal in the center of the plug must have 12 volts to power the unit and to sense system voltage. You can tie that terminal to anything under the hood with that dark green / orange wire. That includes the ignition coil, oxygen sensor heater, or injectors. That way it will turn on automatically with all that other stuff only when the engine is running.
The green wire from the alternator goes to the remaining terminal on the right side of the regulator's connector. Current goes from the ASD relay, through the dark green / orange wire, through the rotating field winding where it makes an electromagnet, through the green wire, through the circuitry in the regulator, through the case to ground and back to the battery. The regulator introduces a varying amount of resistance to reduce current flow through the field. That reduces the strength of the magnetic field and controls output voltage and current.
If you're doing this modification because of an overcharge condition, check for full battery voltage at the computer connector, pin 3 red / white all the time, and pin 51, dark blue / yellow when the engine is running. There will be other problems if either of those are missing completely, but corrosion in a connector pin could lower the voltage just enough to make the regulator think system voltage is too low The regulator can not short completely to full-field the alternator but it could allow the system to overcharge. If you measure battery voltage significantly over 14.75 volts with the engine running, it is overcharging. If it appears to be running full-fielded all the time, look for a spot where that dark green wire is rubbed through and grounding out.
On the Engine Computer, the top row of pins has pin number one toward the front of the car and pin 20 is at the rear. In the center row, pin number 21 is under pin 1, and pin 40 is under pin 20. Same for the lower row. Pin 41 is at the front and 60 is at the back.
Should you choose to remove the black plastic block from the back of the alternator and not use it, the 12 volt supply wire can be connected to either terminal. The other one goes to that terminal on the right corner of the regulator's plug. When you're done, you should find the battery voltage with the engine running is between 13.75 and 14.75 volts.
To avoid confusion I should probably mention the difference in the 1969 and older circuit vs. The 1970 and newer circuit. In the older circuit, battery voltage is tied to the regulator as shown in the diagram, then current flows to the alternator last and it's the alternator that is grounded. Turn the ground and feed around for the newer circuit. Battery voltage is applied to the alternator first, then current goes to the regulator, then to ground. It's the regulator that is the ground for the circuit. Your computer-controlled circuit is the same. Don't be confused by that feed wire to the regulator. It's not part of the field circuit. It's there to power the regulator circuitry and provide the reference for system voltage.
Sunday, October 17th, 2010 AT 11:57 PM