That's a huge difference in voltage between the two terminals which means it's developing a strong magnetic field and a high output. The fact there is some voltage on the control wire proves it is not shorted to ground. The overcharge condition is being caused by the voltage regulator. I'm 99 percent sure everything is in the Engine Computer and replacing it will solve the problem, however, there are two important points to look at.
First, there is a 12 volt feed wire going to the computer that is used for the regulator to sense system voltage. I don't know which wire that is but if that voltage is missing the regulator will think system voltage is low and will keep trying to raise it. Normally that circuit also feeds other things so it can't be missing completely. If the voltage is just a little low, say due to a corroded splice, the other stuff will still work but the regulator will think system voltage is low. Based on the recent history, I'm inclined to think a used computer will solve the problem.
The second thing to keep in mind is there were some vehicles that split the Engine Computer into two parts. The Logic Module sat inside the car behind the right kick panel and received the information from the various sensors. It made the decisions, then told the Power Module under the hood what to do. It was the Power Module that ran the injectors, ignition coil, alternator field, and other relays and solenoids. In that system the voltage regulator in the Power Module can become shorted and cause the overcharge condition, or the sensing circuit in the Logic Module can fail to read system voltage properly or fail to tell the regulator when system voltage is high enough. Unless you can find a wiring problem you might have to resort to just plugging in a different computer to see if it solves the problem.
I'm pretty sure that Logic Module was used on older cars from around '85 or '86, but I don't know how long that system was around.
Wednesday, February 23rd, 2011 AT 3:56 AM