Hey folks, new to the site, been lurking for a while, finally joined up. I've got an issue with my 92, just happened the other day, doesn't seem to be charging. Gauge shows about 12v running & the check engine light came on. I checked voltage at the battery while idling with a multimeter, 12.36v. Shut the engine down & checked again, 12.28v. With my little knowledge of these trucks I think it could be 1 of 3 things: the alternator, the crank sensor, or the ECM. The truck's totally stock (for now) and the speedometer, odometer, and cruise still work so I would guess the ECM's o.k. I haven't done any troubleshooting other than checking voltage so I wanted to get some pointers. I can have the alt. checked, that's easy enough and I guess should be my first check. Any help appreciated.

 

If the A/C and the cruise are still working it's NOT the crank sensor.

The ASD relay is a good possibility you've overlooked. It supplies B+ to the field. It's the front relay in the group of 3 on the driver's fender. Swap it for the A/C relay (rearmost of the three) and see if the truck starts charging again.

 

It could be the alternator or the ecm that is what regulates the charging system. You can have the alternator tested easy but the ecm is about $400

 

Thanks for the replies. It's a non - A/C truck(bummer, I know) so don't have the third relay. The second relay is keyed differently so it won't swap. The speedo wasn't working - it would bounce all over the place so I changed the speed sensor & fixed it. The cruise worked great also. Today the speedo started jumping around again, not as bad as before but not working properly. Cruise still works but surges of course. Can we still eliminate the crank sensor and I should have the alternator tested?

 

If the cruise works the crank sensor is OK. Try a standard Mopar relay, the junkyards are full of 'em.

 

10-4 wannadiesel, will do. Thank You.

 

A relay is nothing more than an electrically/magnetically triggered SWITCH.

Could not the relay in question simply be by-passed to see if that yields the desired function ??

 

The speedo issue could be the yoke nut is loose on the tranny. This only applies to 5 speed 2 wheel drives. Mine was loose and let the speedo gear slip and make eratic readings. Just a thought. Good luck!

 

Sure, but it's easier just to unplug the relays and swap 'em. A paper clip in the right spot would accomplish the same thing, though.

 

Wannadiesel is the Man! It was the relay! A $6 Napa relay fixed my problem. I would have never suspected that, didn't have a clue. I'm pretty good with troubleshooting, pretty handy but wouldn't have known to look at the relay.
Thanks a bunch!

 

Glad you got it working.