the blue with yellow goes back to the ASD relay then on to the ECM.
If this is the case it is the ground to the coil side of the asd relay. The ECM will supply the ground for the asd to come on(ignition on no crank) but go off in a few seconds. It sounds like the ecm is not supplying the ground for the relay to come on. You need to check this with a meter! Put one lead on the positive battery terminal and the other on the blue/yellow wire lead. As soon as you turn the ignition to on you should see battery voltage.
the blue with yellow goes back to the ASD relay then on to the ECM.
If this is the case it is the ground to the coil side of the asd relay. The ECM will supply the ground for the asd to come on(ignition on no crank) but go off in a few seconds. It sounds like the ecm is not supplying the ground for the relay to come on. You need to check this with a meter! Put one lead on the positive battery terminal and the other on the blue/yellow wire lead. As soon as you turn the ignition to on you should see battery voltage.
I get what you are trying to tell him but he should get 12volts from A of the asd, to ground, key on, and able to pass a load test. The blue and yellow must also be able to pass a load test , a meter is not good enough. If both of those will pass the load test, and it runs with that relay jumpered it should be the ecm.
Looking at the diagram if it runs with pin B and D jumpered, or D grounded, it almost has to be blue and yellow wire from pin C to 51, or the ecm.
It's quite possible. They seem to do well for 20 ~ 25 years and go bad in some way, most commonly the voltage regulator function quits. Buying a used one is going down the same road you're already on, buying a rebuilt one is a crap shoot with worse odds. We got one out of Florida for little sisters old van. It's done well, until the van died of unrelated causes.
I think I'm just gonna go ahead and buy another ECM. It'll either fix it, or I'll have a backup for later. They're not getting any easier to find.
Now, do I do the junkyard crawl, buy one from rockauto/ebay, or have mine 'rebuilt'?
Only you can answer that question. I have had decent luck buying pcm both ways. I would at least confirm the blue, and blue/yellow wires can handle a load before I spent my money unless a spare is what you want. In the diesel world the engine computer is $900, so I like to make sure the wires can handle a load, as I have found that problem a lot, especially on the asd circuit.
Slight delay on this. I tried to source an ECM from local PAP yards and kept finding '92 - older or '95 -newer. Six years ago when I bought this thing, Dakotas were pretty easy to find. Now......not so much. *sigh* hindsight being 20/20 and all that.
On to ebay...............
(I haven't load tested yet. It's been to dang hot out).
I found a few used ECMs on ebay and ultimately bought one from a vendor called 'partwheeler' based out of Colorado. I chose them because of price, they didn't require a core, and look to have a pretty good return policy if need be.
I placed my order this past Wed and was told I would get it either Mon or Tues next week..........it arrived today (Fri).
So, right after work, I went over and installed this 'new' ECM.................. The truck fired right up. The truck is still on stands, so I just let it idle for about 10 minutes or so. Even without driving it, I noticed two differences almost immediately, the OD switch works properly again, and the tachometer works again. Hard to tell 100% without driving it but throttle response seemed quicker too when I winged it a few times.
I'll go over tomorrow and put the bed and wheels back on it so I can give it a proper test drive.
While looking for ECM's on ebay, I came across a vendor that rebuilds/refurbishes ECMs (all models) I may go that route with my original one to have it as backup.
Big THANK YOU for all the help with this problem! It is VERY appreciated!
Glad it runs. Be careful who you use to do a reman, some prorate the one year warranty, and only cover what they fix, not the whole unit. Dodge computers can only be opened and unfolded so many times, like 4, then they are junk Anyway fighting with a certain rebuild in Florida, a cummins expert, that claims the pcm we sent is perfect, it will not hold the ASD relay down, that circuit cannot even carry a 100 milliamp load, I asked did you even test it. Assholes, made the kid change the crank and cam sensor, batteries, dodge dealer checked all wiring, they said all good pcm bad, I load tested everything, all good, what a joke these guys are. Have a used one coming. Maybe me asking them did you load test that switched ground, or just use a meter or scope, pissed them off, oh well.
I'll go over tomorrow and put the bed and wheels back on it so I can give it a proper test drive.
Well, THAT didn't happen.......until today. Between my foot issues and summer temps fully kicking in, it just kept getting put off. I'm kinda embarrassed this whole fiasco took 4 months...........
Anywho......
Went over this morning at the butt crack of dawn (8 AM ) and got it all back together before the temps got unbearable again. She runs good! Put about 5 miles on it. I'm guessing the computer is relearning as the truck ran noticeable smoother when I was done.
I have a few other issues I want to tend to before making it my driver again, but its a HUGE load off my mind knowing that it does run and drive once again.
Between my foot issues and summer temps fully kicking in, it just kept getting put off. I'm kinda embarrassed this whole fiasco took 4 months........... 
) and got it all back together before the temps got unbearable again. She runs good! Put about 5 miles on it. I'm guessing the computer is relearning as the truck ran noticeable smoother when I was done. 
