^^^^^ I've been wondering the same thing; just never got around to ask.

A GOOD relay will NOT get stuck.

 

I have seen one where the guy wired all the glow plugs in series...

 

I measured the amps just past the relay. I clamped around the two 10 gauge wires going into the harness, so I was measuring power going to the glow plugs. One 10 gauge wire for each bank. Before I did that though I checked each glow plug connection with the connectors off the glow plugs for voltage. I got 12.6 volts at all 8 connectors on the end of the fuseable wire that connects to the glow plugs.

That is why I am stumped as to my readings for the amperage. I push in the momentary switch for 5 or 6 seconds and whammo...she fires right up.

My momentary switch sends power through the purple wire at the relay and no where else. The power at the purple wire powers the relay, the relay closes and allows power to the other side where the 10 gauge wires go to the glow plugs. All power goes nowhere except to the relay and then on to the glow plugs. The glow plug controller is disconnected. My wait to start light is a different circuit coming off the relay and is only lit up when I push in the momentary switch to power the glow plugs. When I let up on the momentary switch the wait to start light goes out and whammo...she fires right up when I turn the ignition key.

I have checked the amperage 5 times now and get the same readings since I put in the new zd1a's. I have checked my meter to make sure the settings are right and all that. The reason I am going thru all this is to see if I can find a way to prevent glow plug burn up if the relay ever gets stuck again. I am using the one called for and the new one is exactly the same as the old one.

I think if I add an on/off switch next to the momentary switch I can accomplish my **** retention thoughts on this. To add the on/off switch I will add a power post by the relay and put a jumper from the relay where the glow plug power lines are and put the glow plug power lines on the added post. Then run a line to the on/off switch and then back to the relay. That way I have to put the switch in the on position, depress the momentary switch, then put the on/off switch in the off position and start the truck. That way if my relay ever sticks again the switch will turn off the power to the glow plugs. Theoretically I should get many more than 5 years out of my glow plugs as long as I don't hold the momentary switch longer than 5 or 6 seconds.

I still don't know why I only read 20 to 24 amps...Very confusing...One line power 4 glow plugs and the other line powers the other 4...Left bank/right bank set-up. Is that wired in series or parallel? Maybe that's why? Mystery to me...but everything right now is as it was before and like I said I got 5 years service and no telling how long for previous owner.

 

Are you using the clamp to measure both wires to each bank at the same time? I have an AC/DC clamp ammerter too and the readings are goofy if you don't isolate each wire individually. That may help, let us know.

Sent from my HTC ONE using IB AutoGroup

 

That's the standard wiring for the glow plugs to the relay: left bank tied together, right bank tied together, then both to the relay.
So you have the glow plugs on one of the large terminals of the relay, 12v from the battery on the other large terminal, 12v from the momentary switch on one of the small terminals, and the other small terminal grounded, right?
What kind of meter do you have? I've never seen an inductive DC ammeter, but Google shows me they are out there...

 

Poor choice of words on my part
The glow plugs are always in parallel, of course, as they ground through the head.
The guy had daisy-chained the wiring, so that the first segment was taking the full load and burning quickly...

 

Each glow plug should have approximately 0.5 ohm resistance.
Current in amps = volts divided by resistance in ohms, so 1 glow plug draws approximately 24 amps. 8 plugs will try to draw 192 amps.

 

Into what circuit would you introduce the toggle switch? If you're thinking of putting a switch on the main power to the GPs, that's a BAD IDEA. That switch would have to take the FULL current of all eight glow plugs, which, despite what your meter says, if they're wired correctly, can indeed be close to 200 amperes. That's a LOT of power to push not only through that switch, but through wires that pass through the firewall. You'd have to have an EXTREMELY heavy-duty switch.

And of course, it defeats the purpose of the relay, which is to do what relays do by definition, that is, allow a LOW current switched circuit to control a HIGH current circuit. Of course, if you continue down that mental pathway, the next "logical" thing would be to put that toggle switch on its own relay, use the toggle switch to switch the coil circuit, and run the contact circuit in series with the existing relay. But then you're just introducing another point of failure, another relay which could simply fail to close, or if you again choose an inferior piece of junk, might stick closed just like the other one. Rube Goldberg would be proud.

It's still hard to understand what the objection is to using a relay that's up to the task, such as those already listed. Obviously no one has scoured EVERY thread on EVERY forum out there, but in all the discussions I've read about the Stancor and Western Plow relays, I have yet to find a post indicating that either one has ever welded itself closed in the contact circuit.

 

Yeah, putting a switch in the cab between the GPR and the glow plugs is not a good idea...

 

How about hooking your amp clamp around the battery cable before the starter relay?

 

^^^^^^ That would be informative. And just as a "proof of concept" that the meter is reading accurately and not hitting some limit, the OP could put the ammeter on the main battery cable to the starter, and trip the key to START, just to see if it reads the full current draw of the starter motor.