No B+ from ignition to start relay in the PDC. Clutch safety switch jumpered. Blue/yellow wire good right up to the ignition connector. Could it be the connector or most likely the Ignition switch itself?

 

Won't start, or won't crank? Since you mentioned the starter relay, I guess it's no-crank?

Have you tested for continuity across the switch?

 

Won't crank, unless I apply 12 volts to the Blue/yellow wire from the ignition switch. It appears to be in the connector to switch or switch itself.

 

Haven't had a chance to get into the switch yet.

 

Replaced the ignition switch but still not getting 12v on blue/yellow to the safety switch. But if I put 12v on at the safety switch it cranks. If I jumper in 12v on the blue/yellow right at the ignition switch connector I get nothing. Which would seem to indicate a break in the Blue/yellow wire between the switch connector and the safety switch—it's a pretty straight run from the connector to the safety switch but I guess there could be a short or a break somewhere between the two. Am I missing something?

This is the schematic I looking at.

 

If it runs after you manually applied 12V to the safety switch you have power on BATT A1 - if not you lack power to the ignition switch or have a broken switch/wiring issue.

 

Alpine thanks for your comments. Work and holidays are getting in the way of this little project.
I Did install a new ignition switch but still no crank from the key start position. The radio goes off during the attempt as though there's a huge power draw.
I can only crank the engine with the safety switch jumper.
There is no FSS function unless i manually raise the lever and then hold it there. At that point the engine will start and run (with safety jumper in place).
I can't figure out where the blue/yellow wire goes when it leaves the ig. switch connector (obviously not as straight a run as I first thought)
A wiring problem for sure but where to look next?
Would a bad FSS relay be the problem?

Thanks for your help!

 

If the motor will not crank from the key, the FSS is not the problem.
With a bad FSS the motor would crank away happily but with no fuel flow from a closed FSS it would never catch.

 

Thanks Oliver!

 

The radio and all the accessories are shut down while cranking, this is a function of the ignition switch.
The FSS gets a signal to pull up from the starter and a hold up signal from the ignition switch in the run position- if you turn on the ignition and pull up the FSS by hand does it stay up?

A bad relay or a bad fusible link could be the problem with the FSS, but it looks like your ignition switch does not get it's signal through to the clutch safety switch.
This sounds a lot like the wiring loom in the steering column to me, they get pinched and stretched if you adjust the steering wheel often.

 

Ah, good to know that about the Accessories shutting down during start. And, Not sure if the FSS stays up without being being held up—I blocked it up before starting with it with the jumper. I'll check that. I don't seem to be getting any 12v signal on the blue/yellow wire at all. I appreciate the information regarding the FSS activation—that might explain why it starts with the jumper but only runs one or two seconds before quitting. With the FSS lever held up manualy it runs fine.
Thanks again for your help.

 

OK, your FSS is a classic- pull up works, hold current is not there (or the hold coil is damaged, very rare)


The shut off solenoid gets 12 volts from 2 places. Check to see if 12 volts is present at the light green and black wire with the ignition key in the start and run positions. The black and tan wire should show a good ground. The red and violet wire should have voltage when the starter is spinning. Here is more info from the dodge service manual:
With the ignition switch off, the solenoid shaft should be down and the injection pump lever should be in the shutdown position (no fuel supply to injection pump)
Turn the ignition switch to the CRANK (starter engage) position and observe the solenoid shaft and injection pump lever. The shaft should pull up (shaft retracted into the solenoid) and the pump lever should be in the run position (fuel being supplied to injection pump).
Release the ignition key from the CRANK to the ON position. The shaft should remain in the up position and the pump lever should remain in the run position (fuel being supplied to injection pump) If the solenoid shaft is not moving, refer to the following:

So, either you got no power from the start and the run pins of the ignition switch coming through or you have 2 separate problems.
With the engine running do you have the tach showing correctly, do you have charging from the alternator?
Even though the Cummins is quite happy to run with the lever held up by whatever means the Dodge needs a bit more to work correctly (Charge the battery, run the AC and some more stuff)

So I would start by removing the plastic from the steering column and check the wiring from the ignition switch downwards. (And check the ignition switch for continuity in the different positions. )

 

Taking a weather break, it was below zero last night and not too much above that now. We should get a chinook wind in soon and I'll get back on it. I thank everyone for their help and will keep you posted as I go along.

 

FIXED!!

More by accident than anything else but it's something I haven't heard here on the forum before. The large, white, connector block near the steering column was the culprit.
I spent many hours over the last month going over all the usual trouble spots related to my problem and found a lot of potential problems, which I fixed but still couldn't come up with the fix.

Yesterday, I was going back over all the connectors (for about the tenth time) and made sure all were clean and firmly connected when I decided I would take the main block apart and have a look at the wiring. I had pushed on the main connector many times before and everything seemed secure. This time, however, I put a socket on the brass colored bolt in the middle, to take it off, and felt that it was not at all tight. Hmmm! I said, that can't be right, so instead of taking it off I tightened it up and decided to hook the battery back up and give it a whirl. Sure enough, the truck did it's usual instant start and ran like a new one. I spent some time banging my head against the wall before finally deciding it was indeed all worth it. I had cleaned about a million grounds, checked every fuse, relay and solenoid and inspected about ten miles of wiring. I had also replaced the ignition switch (which was original), cleaned and lubed the FFS, ripped out and replaced a rat's nest of wiring from the last owner and redid all the battery terminals.

With 308k on the clock this truck doesn't leak, or use a drop of oil (ever) and has never left me alongside the road. (it failed this time in the carport next to a garage full of tools). For eight years I have never had this truck turn over more than two revolutions before it would roar into life, freezing temps or not. I'm happy to report it's that way again.

Whether that connector bolt loosened on its own or was left loose by the last perpetrator I will never know. But it's a super easy thing to check and could save someone a lot of trouble down the road.
I thank everyone who contributed to this thread.
I'm off to put another 300k on this truck...grin!