Have a friend with a 1990 d250 cummins and is having charging system problems. The truck will not hold a charge. We have relaced the altanator and voltage regulator. After changing the v/r we put a voltmeter across the battery terminal and after starting the truck you can watch the system start to charge. After about 20 seconds it reaches 14.2vdc then all of a sudden the voltage drops to 12vdc(not charging) and one of the wires going to the positive terminal starts to get really hot. Have to shut the truck off to keep wire from getting to hot, let cool, then same happens again. Any help at all would greatly be appreciated.

 

Which wire? Which positive terminal? If it's one of the wires to the battery positive, perhaps you have something putting a dead short on the battery. Basically, the alternator connects direct to the battery because the diodes in it will prevent back flow. The regulator hooks to the field terminal of the alternator, and a sense line from the regulator connects to batt positive. When the voltage gets up to the regulator preset, the regulator reduces the field current to prevent overcharging.

Make VERY sure there is a good ground on the alternator and the regulator. Otherwise look for a short circuit somewhere. Have you tried another battery?

Edwin

 

Its one of the small red wires going to the positive terminal on the battery. Also tried differant battery.

 

It kind of makes me wonder if you have a bad ground on the voltage regulator. If you have a bad ground it will take out the regulator real quick. Also make sure you have a good ground on the alternator.

Edwin

 

We ran a jumper wire for a better ground for the voltage regulator this got it where it would charge for 20 sec. Will check ground on alt and see what happens.

 

Sounds like you may have toasted the VR. Glad they're only $12.

Edwin

 

Here's a diagram:

 

Thanks for the wiring diagram, this is what we need to check continuity for the charging system. I think we might have a short going to the ignition switch.

 

I'm working on a 1990 d250.
I believe i have a problem with the two wires going to the ignition switch, can i cut those wires going to the ignition and splice into another 12v line that only has power when the key is in the on position?

 

Hi I have changed alternator ,still not charging could be computer or crank sensor ,can't get either checked so i want to install external voltage reg ,can i use the diagram shown or is there another way to do it without getting into exsisting wire harness. all help appreciated Ole

 

The above diagram is for a 1989- 1991. By your post i guess its for a 1997. Your voltage reg is in the PCM. There is a differant diagram for adding a external voltage reg. i think it is in the tech facts section or try the search for external voltage regulator. Check this tread out it should help.

https://www.dieseltruckresource.com/...tage+regulator