Glow plugs always getting power!?

[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.

[rammertide07]

Cody, here is a thread I did on TDS..made a post each time I found a new piece of info. Takes too long to type all of that out on my phone so figured I'd share the link. Please note that the initial test of the relay showed it was putting out .7v before I ever did anything with the wiring. Then after digging deeper it showed I was getting 12.5-13v.

GPR continuity question - Diesel Forum - TheDieselStop.com

[cleatus12r]

Originally Posted by rammertide07

Please note that the initial test of the relay showed it was putting out .7v before I ever did anything with the wiring.

So that was between the ground terminal of the battery and the post of the GPR that has the yellow and brown wires?

Normal. You're measuring voltage drop across a resistance (glow plugs).

[rammertide07]

Originally Posted by cleatus12r

So that was between the ground terminal of the battery and the post of the GPR that has the yellow and brown wires?

Normal. You're measuring voltage drop across a resistance (glow plugs).

After I hooked everything back up, I measure the relay output again. The volt meter was reading 0v on the second go-around....first time it was measuring .7v.

I appreciate all your help and time. I know some mechanically inclined people that can give me some hands on explanation. Just talked to an ASE mechanic, now he's confused

The way I'm looking at it, the glow plug side of the "tree" is a dead branch...not connected to any type of power source, since the negative cables are not connected. The "glow plug feed" side of the circuit is not suppose to have continuity with the + side of the batteries until the GPR is engaged. Thats the way I look at it...

I'm going to do some research on automotive 12v systems and relays.

[cleatus12r]

Because you don't have the negative battery hooked up, some of the circuits/accessories that are on the constant (non-keyed) power side of the truck WILL conduct B+ voltage all the way through.

Since the volt meter draws VERY LITTLE current, you WILL see battery voltage regardless while doing a VOLTAGE DROP TEST (which is what you're doing; even if not on purpose) because the positive voltage doesn't just say, "Gee, I guess I'd be trespassing on Negative's property if I actually went through this circuit since he's not here.....".

Seriously, if your ASE mechanic buddies don't know anything about voltage drop tests (or theory), they better stick to tire rotations.


Edit:

I'm not trying to come across as a jerk, but why in the world are you chasing something that is not a problem?

[rammertide07]

Originally Posted by cleatus12r

Because you don't have the negative battery hooked up, some of the circuits/accessories that are on the constant (non-keyed) power side of the truck WILL conduct B+ voltage all the way through.

Since the volt meter draws VERY LITTLE current, you WILL see battery voltage regardless while doing a VOLTAGE DROP TEST (which is what you're doing; even if not on purpose) because the positive voltage doesn't just say, "Gee, I guess I'd be trespassing on Negative's property if I actually went through this circuit since he's not here.....".

Seriously, if your ASE mechanic buddies don't know anything about voltage drop tests (or theory), they better stick to tire rotations.


Edit:

I'm not trying to come across as a jerk, but why in the world are you chasing something that is not a problem?I understand you are not being a jerk. In my head it is a problem just because I don't understand. I am understanding a little bit more now...just trying to wrap my head around it. I really wish I had someone in person that could explain it to me, hands on. Hands on experience always beats text book experience. I've accpeted that everything is as it should be. It just bugs me to not know why...

. . . . .

[cleatus12r]

Originally Posted by rammertide07

But where is the + voltage coming from the glow plug side of the open circuit.

Between every circuit in the truck that is on the power distribution "tree".

You're looking way too far into this.....
It's easy.