I used a test light to indicate the battery wires (two heavy gauge yellow wires) terminal at the glow plug controller were hot.

The ignition wires (two light gauge red wires) terminal at the glow plug controller were hot after I turned the ignition key for the Wait To Start Light.

The glow plug wires (two heavy gauge brown wires) terminal at the glow plug controller were not getting juice to heat the glow plugs?

Question: Could this issue be caused by the Glow Plug Controller, or the Glow Plug Relay located under the Glow Plug Controller?

Thank you in advance for any help.
Scott

1988 F250 7.3 Diesel (Stock) C6 Auto, 3:55

 

If you want the GP controller test email me.... click on my name.

Please use........ SUBJECT: GP controller test

 

 

If I'm reading you right you have power from batteries to relay, and the relay control wire is hot when the key is on. However you get no voltage at the relay output terminal - even when the control wire is re-attached to the relay and the key is on?

If that is the case your GP relay is dead. I bought a Niehoff brand replacement at Napa for $16 and it has worked fine for a couple of months now. You can spend 3 or 4 times that much for one if you want to go to the dealership or something....

 

Thanks CheaperJeeper,

I'll pick one up!

Scott

1988 F250 7.3 Diesel (Stock) C6 Auto, 3:55

 

Did you test the glow plugs?

On an 88 which has the new style system, several burnt out glow plugs may cause the controller to not even try the glow plugs.



Use a wire and ground the white terminal for just a second or two with the key in the ON position. If the relay clicks, you should have power to the glow plugs and the relay is not the problem.

Also check the ground wire and make sure it is making contact with a good ground.(Remove and clean the terminal and area around the bolt where it is clamped)

 

GOOD POINT Dave. I didn't notice the year on his. That $16 Niehoff unit I got at Napa won't work for an '88 - and the newer one is probably more expensive.

Sorry if I mislead you Scottie250. My bad....

 

Thanks Dave,
I tested all the glow plugs after viewing the testing procedure. Test light clipped to the positive terminal while touching the top of the glow plug. The test light came on with all eight plugs, all are new Motocraft plugs.

I will try grounding the white terminal with the key turned to the on position, thanks.

You mentioned checking the ground wire connection, I have a little embarrassing story about that...
I replaced the glow plug/controller harness. While in the process, the ground wire dropped to the back of the controller after disconnecting it from the controller. It was still connected on the other end. My problem was I did not see which terminal it came from? After looking at the bend in the ground wire, it appeared it was bolted to the same post as the two large brown wires leading to the glow plugs? I viewed the same picture you posted of the controller from somewhere on this site, and still cannot see which terminal is for the ground?
Thanks again,
Scott

CheaperJeeper wrote;
Sorry if I mislead you Scottie250. My bad....

No,no, thanks for the help. You were simply sharing one of your experiences that helped you in a similiar situation. I was too busy at work to pick one up today anyways. May need to pick one up later just to keep the truck reliable.
Thanks,
Scott

1988 F250 7.3 Diesel (Stock) C6 Auto, 3:55

 

The black ground wire needs to be attached under one of the mounting bolts that are in the intake manifold.
No ground to the controller, no ground to make the relay work.

When the controller wants the glow plugs to turn on, it passes the ground connection thru to the white wire. This completes the circuit to activate the relay.