I have a 1992 D250 2 wheel with 75,000 miles new battery , I pulled the altanator and took to a altanator shop it checked good. The truck is clean no rust. Ground wires all seem good. Truck came new with a cigarette lighter and a dome lite. Some say the crankshaft censor is what signals the ECM to regulate a charge. I checked it and it is faulty. I.have one ordered from Rock auto parts. Does any one know if I'm going in the right direction. The Dodge dealer said it needs a new ECM. Thanks if anyone could give a worder of advice. I know that I could install a regulator .

 

Personal experience here is you are most likely not dealing with an ecm issue. Crank sensors do go bad, and easily replaced, but in the words of Mr. J., proper diagnosis goes much further than just swapping parts.

We have the sticky here (top of page) and in the electrical section, there are easy tests to help your diagnosis.

Pull the asd relay and swap it for another relay and then use a multimeter to see is you get 13.8 volts Or So at the battery cables. If so, the relay needs to be replaced and you're done.

The sticky has pictures and diagrams explaining this.

Besides the crank sensor and asd relay going bad, the fusable link failing can do the same thing. I was driving along, and all of a sudden it wasn't charging anymore. Took me awhile to find the FL was broken internally without any outwards appearance of buring through. Another good read in the sticky

 

I have found some post on line that claim the CPS Signals the ECM that the engine is making rpms to regulate a charge. Some claim if it stops regulating a charge to red place the ECM

 

Don't automatically replace your PCM, as has been said diagnose it.

And yes, without a properly operating engine speed sensor your PCM will not know it needs to charge.