This 1987 Dodge Dakota came in with the complaint of the battery going dead while driving. After checking the system at the battery with a volt meter and amp meter, I went to the voltage regulator on the firewall to start testing. I don’t get a chance to work on something this simple very often and it was kind of fun. First I disconnected the regulator with the key on and checked for ignition power on the dark blue wire and it was present.
Next I checked for bleed through power on the green field wire and it was not present. These connector sometimes burn out. To order a replacement harness please click here.
I then checked the wires at the alternator. Power was present on the blue field wire.
Voltage was also present at the main battery post on the rear of the alternator.
Again there was no bleed through power on the green field wire.
Time to remove the brushes for inspection.
Sure enough the brushes were worn out.
Now for some charging system basics. The charging systems on Chrysler, Dodge and Plymouth vehicles from the early 70’s to the late 80’s used alternators with brushes that were completely insulated from chassis ground (sometimes referred to as above ground). An ignition power signal was sent to one of the brushes and to one terminal of the voltage regulator. The second terminal of the regulator sent a variable ground signal to the other brush. Both brushes connect to the rotor slip ring which are then connected to the field wire wrapped around the internal core of the rotor. As the regulator is the end termination of the field circuit, If the field circuit is complete through the wiring and the alternator I should of had power at both terminals of the regulator connector with the regulator unplugged. I did not have power on both and that is why I proceeded to the alternator for more testing.