1991 7.3 non turbo glow plug problem

[Kenny D]

I am trying to find out how to troubleshoot my relay system. AS YOU LOOK at the solenoid from the front of the truck. The upper left has the hotwire from the solenoid on left wall in vicinity of battery, always hot 12v. The next terminal over has the red wire from the solid state mod on it and a red wire with green stripe that when the key is turned to on has 12V and also powers the other small terminal to 12V also. I do not get power on the lower right hand brass terminal which I read could be caused by lack of resistance?
I believe that I have a homemade glow plug wire harness and do not know what to check next?
How do I check to see if the relay and module are working correctly?

I have pulled the glow plugs and continuity checked and resistance checked them continuity good resistance .4
Resistance checked the harness and also got .4

Before I go throwing parts and dollars at it I would like to make sure I have correctly identified the problem

 

[franklin2]

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The terminal with the "white" wire is the one from the controller brain. If you have 12v from the ignition switch, (the red/green) then when the brain grounds the white wire, that puts power on the coil of the relay and will make it click. When it clicks, it connects the yellow battery wires to the lower right terminal where the glowplug wires are connected, giving power to the glowplugs.

If you still have the white wire connected, and get no click, pull the whole mess up and check the ground wire for the system. I believe it connects underneath or behind and has been known to give problems like all grounds seem to do.

If you want to do a quick test, take the white wire off and tape it. Then get a short scrap piece of wire, hook it to the terminal where the white wire was, and with the ignition key on, take this scrap piece of wire and touch it to something metal on the engine, The relay should click and you will have power on the glowplugs. Don't over do it and burn your glowplugs out. This is how the manual conversion works. You run a wire from the white terminal into a pushbutton in the dash and then run the other side of the pushbutton to ground. When you hold the pushbutton in, it grounds that terminal and with the key on, will glow the plugs as long as you hold the button in.

 

[Kenny D]

Thanks will try on Wednesday, its the next time I will have a chance to work on it. If that doesn't work just going with the bypass its not only the cheapest solution but sounds like it will last.