I have a 94 regular cab 12 valve that I bought used 5yrs ago and I have had numerous electrical trouble with it since that time. Current problem started out like this: after engine got to operating temperature or if ambient air temp was more than 80F the tach quit, no AC, no alternator, no overdrive. I drove truck like this for past 8 months, worked fine in winter, I figured whatever was causing trouble wasn't getting hot enough. A few months ago now, all of the red dash lights started flashing off and on and sometime stay stuck on. When these lights flash, I also lose the tach, overdrive, ac and alternator. When those lights flash, I can hear all of the relays under the hood clicking in and out (if hood is open and u are listening). I replaced speed sensor on crankshaft yesterday, lights still flash when brought up to temp, but after driving 50mph for a mile or two, lights quit flashing and everything works. I am sure I have a connection/ground issue somewhere, but am looking for a little guidance as where to start. I also do not know what to make of the fact it needs to be hot to quit working. I was hoping that speed sensor was causing all the trouble. Nope. I would appreciate any advice. Thanks

 

Check the wires, connector and gap for the engine speed sensor.
If they seem fine replace the sensor, auto parts store part.
If the ESS isn't functioning correctly the computer thinks the engine isn't running, nothing electronic will work.

 

I replaced engine speed sensor yesterday, have not checked gap with gauge yet, but it does read rpms and seem to work properly until the engine gets up to operating temperature. I will recheck air gap with feeler gauge as soon as I can. Thanks

 

Checked gap today on Engine Speed Sensor, wasn't off too far. Used this pickup to haul cows most of the afternoon, as soon as engine got up to temp 190 or more, I lost tach, AC, alternator and overdrive. Drove pickup that way all day today, last run of the day, I hauled 11 cows 18-20k with trailer, 50miles one way, no OD or anything whole trip with the load on. By the time we got cows dumped and headed for home, ambient air temp dropped dramtically. Down to high 60's compared to upper 80s. I got 4 miles down the road, and the check engine, water in fuel, wait to start and trans temp lights all came on. Those lights stayed on (no flashing) for 30-40 seconds then went off, I got overdrive back, along with alternator and all the rest. Drove pickup another 45miles after the od came back, no problems.

So my questions are: Does anyone have any idea where to start on this? I have talked to my 2 mechanics I use on these Dodges and they both are out of ideas. Any advice would be greatly appreciated. THanks

 

It sounds like a faulty PCM (computer) but that's not the kind of part you want to throw at it $$$.
Plus they rarely fail.
If you know someone with a '94-'95, hopefully with an auto, swap PCMs and see what happens.