My glow plugs quit working, purple wire has voltage, but not enough amps to work the selonoid. What could cause that? 86 f250 6.9 c6 4x4 hell yea!

 

The solenoid requires almost no amps to trigger.

Does the black small wire across from the purple wire go to a good ground?
If you touch a wire from the positive battery terminal to the terminal the purple wire was on, does the relay click?

 

I tried the selonoid from the hot at the battery, it works when I do that. Could it be the temp sensor at the back of the block? How do I check that?

 

The test procedure for the old style glow plug system is about 3.5 pages long in the Haynes Diesel engine manual #10330.

There are several pictures of what terminals are where, I could never describe what to put where, so if you want to trouble shoot the controller you need to find the book.
I have seen it at both Advance Auto and Autozone for about 20 dollars.

When mine died, I went through about 1/2 the procedure, threw the book down and converted to manual glow plug control.
That was 10 years ago.
At that time a new controller was 165 dollars, they can be found for around 100 now.
Mine will stay manual control, I like it better that way because the glow plugs last longer.

I found a fuse in the fuse panel that was only hot when the key is on.
Run a wire from the fuse to a momentary switch.
From the other terminal of the switch, run a wire to the terminal the purple wire was on.
The wire can be a small gauge wire like 16 AWG, it only has to trip the relay.
That is all there is to the conversion.

To operate, turn the key on, press the switch for 10 seconds, start the engine.

Where the longer glow plug life comes from, if the engine is warm, you don't need the glow plugs at all.
It was 5 degrees here this morning.
I went to the shop for a while before going to the job site today.
The shop is far enough away, the engine was at operating temp when I got there.
The engine started just fine two hours after I shut it off with no glow plugs.

Went to lunch four hours later, hit the glow plugs for 6 seconds, and it fired right up.

My guess is the controller is dead, good luck getting it out of the head without breaking it off.
Since it goes into the coolant jacket, if it breaks off you have to remove the head to get it out most likely and you will probably be losing coolant when it breaks off.

That was the other part of why I converted to manual and stayed that way.

 

I replaced my controller 2 years ago when I bought my 84, no problem at all, except the cost. I had put new glow plugs and a new relay on already, when that didn't work, I went with the controller, the glow plugs don't work again, and since putting in the controller it has burn't them out 3 or 4 times, so I think its holding them too long, I'm going back to the manual system, I can count to ten when apparently that stupid controller can't, I hate something that thinks it knows more than me, like when I borrowed my dad's powerstroke the other day, right after an oil change and the service engine light keeps coming on, I hate those stupid computers.

 

I have seen one twist off before the threads broke loose.

When mine died, it did not budge.
But after watching a buddy twist his off, I did not pull on the wrench very hard.
Plus at that time they were 165 dollars which I though was outrageous.

Manual conversion was 10 dollars and 20 minutes time.