Glow plugs always getting power!?

[rammertide07]

I have both negative battery terminals disconnected and have already pulled the gpr. I can touch the ground lead from the volt-meter to the negative battery terminal and the positive lead wire to the wire that feeds the gp's (wires that get voltage when relay is engaged) and I get 13v. Doesn't that mean my gp's are getting voltage akl the time?

Batteries haven't failed in the 3yrs I've had them, but starting is a little slow. GPR is about 8 months old.

[cleatus12r]

No.

That means you're completing a circuit through the meter.

If your glow plugs were "on" all of the time, you wouldn't be able to let your truck sit more than 10 minutes at a time without draining the batteries (not to mention it would stink like hell after a while).

[rammertide07]

Thanks for the reply Cody...both of them.

What circuit am I completing? Shouldn't I be getting 0v since I had the gpr out? Again, I'm probing the wires that go to the glow plugs...not the wire from the battery.

I put the GPR back on and wired it back up...pcm ground is still unhooked. I hooked up one of the negative battery terminals and tested for voltage again at the "glow plig feed" wired. This time I got 0v. Doesn't make sense because I was getting 13v just minutes before at the "glow plug feed" wire.

[cleatus12r]

Yes, it does make sense.

With the batteries' grounds disconnected and you using the DVOM to engine ground (glow plugs) and the battery ground, you are completing the ground circuit to the truck. By reinstalling the negative ground cable, you are no longer completing a circuit to ground through the glow plugs. The technical term for what you have experienced is called "voltage drop".


I'll draw a diagram and you tell me whether or not I'm correct in how you have the DVOM hooked up.

[cleatus12r]

Here's the diagram that I came up with (15 minute drawing in MS Paint). The blue lines are the DVOM leads and they are labeled next to the picture of the DVOM. Also notice the broken battery cables above the negative terminals.

Is this correct?

If this is how you had your DVOM hooked up and how the truck wiring was configured, then what you see on the volt meter is exactly what should be showing on the volt meter.

[rammertide07]

Yep, thats it. But where is the + voltage coming from the glow plug side of the open circuit. Also, when I had the GPR out I was getting continuity between the "glow plug feed" wire and the positive battery terminal.