bcfords,
Look at the relay on the passenger side inner fender.
Make sure the ground wire is on a good ground. Small black wire on small terminal usually closest to the fender.

With a test light have someone turn the key on while you are touching the small purple wire straight across fron the ground wire. Should have power there when the glow plugs are supposed to be ON.

Large terminal near the battery, should have constant battery positive voltage.

Rear large terminal with two large orange wires and a small black wire with a pink stripe if I remember right. This terminal should be hot when the glow plugs are supposed to be ON. (The black and pink stripe wire is what lights the "Wait to Start" light in the dash.)

To test the relay, jump a wire from the battery positive terminal to the terminal with the purple wire on it. Battery voltage applied there should close the relay and turn the glow plugs on.

Next thing to check is near the dip stick look for a connector that should be white in color. It has the two big orange with white stripe wires and several smaller ones.
Examine the connector for signs of overheating on the side the big orange wires are on. If it looks overheated the connection for the glow plug power is probably not a good one. The large orange wires are for glow plug power from the relay to the engine harness. Several years ago mine melted and kinda acted like yours.

I cut the two orange wires as close to the connector as I could and spliced them with a copper split bolt and taped them up well so the did not short out. What a difference it made in the way it starts.

Also on the old style system the controller is in the rear of the passenger side head.
Make sure they did not dislodge the cap with the wires in it while messing with the AC.
The evaporator is right beside the glow plug controller and so is the AC dryer.
You squeeze the sides of the cap and lift straight up to remove it. There are arrows on the cap to show where to squeeze to release the catches.

If you want to install a manual switch on the glow plugs, run the power to the terminal with the purple wire on it on the relay to turn the glow plugs on.

I like to use a power sorce that is only hot when the key is ON. That way kids playing with switches in your truck can not burn the glow plugs up.

 

Dave thanks for all the info, [Im amazed at your patients, I know your much repeated info you give to us novice IDI owners!] I rewired some fuse links, and the orange wire you desbribed...nothing, grounded controller to the battery, put relay from 86, nothing! The only thing I didnt do was replaced the contoller. So Ive hot wired a "starter" push button,[took a whole 25 minutes] works like a dam! And the funny thing is the system is working just fine again, cycling and whole nine yards, but when it doesnt, Ill push that button, again thankyou gentle for all your input!

 

Until I get my GP problem fixed I found if I plug in my block heater for at least a few hours (or over night) it fires up no sweat. Never had problems during the day either...good back-up

 

yeah Daves the man!!

 

Yes - all the truck needs is some heat and it will fire. I had to do the same thing on vacation in Florida. Had to change a controler in a rv park on vacation in good clothes. (ruined them)

 

I had to laugh when I read that, sooooooooooo many times my wife has let me know that I ruined a pair of good clothes. so now I just let her know that I have made a new pair of work clothes.