So ... quick history on my 6.9. Had system working last winter, then one day, WTS stops illuminating. I figure the controller is bad, and wire a push button. I only spliced the push button into the purple wire, and didn't actually cut the wire (basically, the controller AND push button are connected, mostly cuz I liked seeing the WTS button when I push the button.)

This morning, no start. Sounds like I only have 1 cylinder trying to fire. Check resistance on #2 plug, just above 2 ohms, check resistance on #1, infinite.

Ordered new Motorcraft plugs from Rock Auto for $85 including next day delivery and 5% coupon code(SWEET DEAL!).

This got me thinking. Could my controller have stopped working due to the GP's being burnt out? I know this usually fails in the on posistion, but mine seemed to fail in the off position. I guess I'm wondering if it might start working again once I put in 8 new plugs. Thoughts?

Another interesting side note: When I was checking the resistance on the #1 glow plug (which measured infinite), I forgot to hook it back to the connector when I tried firing the engine. Without #1 hooked up, the engine would not fire at all. Hook #1 back up, that one cylinder acts like it's firing. This leads me to beleive that it's the #1 GP that is working. But everything I have read says that the resistance on a good plug is below 2 ohms. What am I missing here?

 

First, infinate resistance should be a burnt plug, open with no conductivity.

May cheaper meters will actually show a dead short, 0 ohm's resistance on good glow plugs.

Ideal resistance is between .5 and 1 ohm.

You said purple wire, so I assume your truck is 86 or older.

Power to the purple wire to close the relay.
On the large terminal with the two orange/green stripe or orange/white stripe wires, you will see a smaller wire, black/ pink stripe that goes to the "wait to start" light.

It is also very possible that the solenoid/relay is bad.
I just replaced the solenoid/relay on my 86 last year at just under 500,000 miles, must have been a good one from the factory.
Cost about 30 dollars.

I have a volt meter installed, when I was hitting my manual switch, the voltage was not dropping even though I knew all the plugs were good.
So I found if I kept pushing the momentary switch, the relay would eventually make contact when the contacts closed and the glow plugs would heat.
Volt meter drops about 2 volts when the relay makes contact.

Check all your plugs, my guess is you have several burnt, probably because the controller turned them on while driving and you did not see the light on.

Also pay close attention to the connector circled in red.



If the connector looks like it has been hot, melted and deformed plastic on the end with the two large orange wires, you have a problem there with corrosion.

The only fix is to cut both orange wires close to the connector on both sides of the connector and splice them together around the connector.
You can leave the rest of the wires in the connector, they are all rather low amp loads, so they do not melt the connector like the orange wires do.

Last possibility is the light in the indicator is burnt out.