Help! Truck no start!

[elminero67]

Need help: for only the second time in 5-6 years, my truck won' t start. I suspect it is the glow plug relay as the glow plugs are not getting hot.

I do not understand how this thing works.

It gives the normal click after turning the ignition, then gives a second click in about ten seconds, just as it always has. Except that it doesn't fire. ( turns over fine, no air on fuel)

I jumped a line from the battery to the relay, only to find that the wire to the relay is ground, not positive. The line to the glow plugs is also ground (negative), as are the glow plugs. Is this supposed to be negative? If so, how does it create a circuit to heat the glow plugs?
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[dn29626]

See if the IP is stuck in the off position?

[elminero67]

Good guess based on the limited info I gave, but it looks like the IP is functioning correctly.

I didn't mention it, but it will fire and run perfectly with a squirt of starting fluid. I did this once, but don't want to resort to this.

It has oil.

Pulled the glow plugs, they look to be in good shape and worked on a bench test.

What I'm still trying to figure out is why the line going the glow plugs is negative?/!

[dn29626]

When you say "bench test", do you mean you removed each glow plug from the engine and hooked - & + to them and they got hot?

While installed in engine, did you jump a wire from the battery + to the glow plug connecting wires?

[elminero67]

Perhaps "bench test" is an exaggeration: I hooked up a ground wire and a + to the glow plug and it got fricken hot very fast. Pret'ner set the wooden bench on fire after a few seconds...

Previously I had tried running a jump wire to the glow plug relay (output to the plugs) and it shorted out. I tested the jump wire directly to the glow plug. It also shorted out. I then tested both with a test light, and both are indeed grounded (negative).

I then disconnected the plastic plug between the glow plugs and the glow plug relay. This solved the problem: I was able to use a jump wire without shorting out, the glow plugs worked and the truck started at the first click of the starter.

It would seem that I have a short between that connecter and the glow plug relay-or the relay is fried.

I will poke around a little bit later when it cools down outside, but I believe I've got the problem narrowed down to the point even a knuckledragger like myself can stumble through it.

Thanks for the help!

[dn29626]

Some relays are wired through the ground side.

[dn29626]

Some relays are wired through the ground path.
Good you got it running.