1991 Dodge Dakota • 190,000 miles

I bought this truck new and have now bought 5 ECM's for same. The problem is always the same. There is no problem with the running of the truck, it is always the charging system. Why does this unit always quit charging my battery?
July 3, 2012.

The voltage regulator is built into the computer and actually causes extremely little trouble. Worn brushes inside the alternator are more common and will cause intermittent operation. If simply replacing the computer always solves the problem, I would look closer at the terminal in the connector to see if it is spread or corroded.

Jul 3, 2012.
It doesn't seem like there would be a likely other problem in this unit. When I replace the 'black box' everything works fine for anywhere from a year to two or three years. Nothing changes, no new battery, no new alternator, no new drive belt. Everything works great until it just decides to no longer charge my battery. I install an new 'black box' and its fine again for however long it decides to work.

Jul 9, 2012.
The only other thing I can suggest is to be sure the fresh air tube is in place. That draws cooling air over the aluminum fins of the heat sinks inside the computer.

You might consider having the alternator load tested. If it shows "ripple" is very high, and the most output you can get is one third of its rated capacity, (30 amps from the typical 90 amp alternator), it has a bad diode. The voltage regulator would cause higher than normal field current to flow continuously in an attempt to raise the output current to meet demand. We're only talking about increasing field current from an amp to as much as three amps but that might be enough stress to eventually cause a part to fail.

These voltage regulators really are very trouble-free so you have to look for some unusual cause to the repeat failures.

Jul 10, 2012.