FIXED (I think): Solenoid feed wires hot, and voltage drop

[Mad Maxine]

Howdy.
The feller that had this truck before me put in a manual glow plug circuit consisting of a momentary-on switch in the cab and a solenoid under the hood. I just replaced all of the glow plugs with Motorcraft plugs, and put in a new glow plug wiring harness (the old harness wire insulation was cracking and falling apart). After I finished the job, I was getting no cold start in the mornings. In troubleshooting the glow plug system today, I first found that I wasn't getting any voltage on the switched side (glow plug harness). So, I redid the connection at the solenoid and glow plug harness with serrated washers for a better connection. Now I'm getting 9v on the switched side of the solenoid, but the feed wires (original Ford harness wires) to the solenoid and feed side of the solenoid are getting really hot. The glow plug harness wires on the other side of the switch aren't hot, I'm just getting a voltage drop.
Bad solenoid?
P.S. -- once when I hit the switch (using a hand-held button switch connected under the hood), I heard a high-pitched buzzing/squealing sort of sound. I'm guessing it came from the solenoid. Never heard one do that...

 

[Indadesert]

I’d put it all back to stock. The stock system works very well and is easy to wire.

 

[IDIBRONCO]

I'd guess that it's a bad solenoid. I've heard some 7.3 style solenoids make a high pitched, low volume squeal, but they seemed to work fine. Maybe they were on the way out. I only saw then used once or twice before the truck left our shop. With all of the low quality parts that people report buying these days, I'll never leave the stock glow plug set up on one of my IDI powered trucks. Mine will be manually controlled.

 

[ihc1470]

Howdy.
The feller that had this truck before me put in a manual glow plug circuit consisting of a momentary-on switch in the cab and a solenoid under the hood. I just replaced all of the glow plugs with Motorcraft plugs, and put in a new glow plug wiring harness (the old harness wire insulation was cracking and falling apart). After I finished the job, I was getting no cold start in the mornings. In troubleshooting the glow plug system today, I first found that I wasn't getting any voltage on the switched side (glow plug harness). So, I redid the connection at the solenoid and glow plug harness with serrated washers for a better connection. Now I'm getting 9v on the switched side of the solenoid, but the feed wires (original Ford harness wires) to the solenoid and feed side of the solenoid are getting really hot. The glow plug harness wires on the other side of the switch aren't hot, I'm just getting a voltage drop.
Bad solenoid?
P.S. -- once when I hit the switch (using a hand-held button switch connected under the hood), I heard a high-pitched buzzing/squealing sort of sound. I'm guessing it came from the solenoid. Never heard one do that...

Question what vendor did you get the Motorcraft plugs from? Define really hot. The glow plug system draws close to 200 amps when they first start heating. You will get a voltage drop as Ford did not use large enough wires for that load. My understanding is they were wanting to lower the actually voltage that the plugs would see. They did that by using undersized wiring which shows up as the feed wires getting quite warm. Sounds like you have a voltmeter so you could do some voltage drop testing and see where the issue is. Test the voltage drop across the solenoid when it is energized will tell you the condition of the contacts. Then test the drop of the wiring from the solenoid back to the power source. I assume this is the same truck you had in the other post below so a 6.9 correct. Been way to many years since I had a 6.9 so this may not be correct. On the 7.3 there is a connector around the alternator area of the engine that the glow plug wires pass through. The glow plug wire connections like to heat and melt that connector due to poor connections and high amps. Most get wired around to solve that issue.

Did plugging the block heater in help with you starting issue? Is that the reason you replaced the plugs?

 

[Mad Maxine]

block heater doesn’t work.
Motorcraft plugs are from Ford Motorcraft distributor.
I had already replaced the plugs when I initially posted about my cold start problem.
The feed wires get hot enough that I could smell burning plastic/insulation. Not so hot I couldn’t touch the wires, but the solenoid lug was no-touch hot. Maybe it’s the solenoid burning up. But the wires were definitely hotter than I’d care for them to be.
What voltage do the glow plugs need to get, according to Ford? 9 volts?
Maybe it’s working as designed?? Except maybe for the cheapo solenoid that can’t handle the current?
Also thinking maybe I have an insufficient ground for the solenoid.

 

[ihc1470]

https://www.ford-trucks.com/forums/1029056-6-9-7-3-idi-diesel-tech-info-3.html

Lots of information on glow plugs on that site. If the solenoid post was that hot I think I would change it. Sounds like the contacts inside are about shot. Is any of the glow plug controller wiring left and if so which system. What type of solenoid do you have now? Is it for glow plugs or a starter or something else? If I recall when I replaced my ZD29 plugs the package said 10.5 volts.

 

[DougBoy66]

I have been using this one from Diesel Rx for quite a while. No issues with it

You must be registered for see images attach

 

[Mad Maxine]

I think my problem was two-fold: first, the glow plug harness wasn't making good contact with the solenoid, which was my first problem. Second, the solenoid that the previous owner had installed was woefully lacking and simply didn't have the grunt to carry that kind of current, which was frying the solenoid and everything before it. I looked up the part number for the applicable glow plug solenoid, and it is Borg-Warner P/N BWDGPR7 or Carquest P/N GPC1003. Just so's you know, the "S" terminal is for the switch (in my case just a SPST momentary-on in the dash) and the "I" terminal goes to ground.
I still have 9 volts on the other side of the solenoid, but by what I can glean, that is the voltage (more or less) that Ford designed the glow plugs to get by way of using undersized hot feed wires (two yellow wires) to get a voltage drop. The wires still get warm, but not nearly as much as they did before.
I say I "think" I fixed it, because I was able to get the truck started cold, and I haven't been able to do that before at any ambient temperature. I pressed the pushbutton in the cab and counted to 10 and she fired right up. That said, it's 75 degrees here right now, so the real test will be when I try to start it when it's 30 degrees outside.
I appreciate everyone's help!
Thanks!

 

[rreegg]

I have a manual GP setup and it makes a squeal when pressed.. it operates fine and was done by previous previous owners… have always wondered if it was standard but never had much reason to ask

 

[franklin2]

If you can believe my dash gauge, when I glow my plugs on my 89, the dash gauge drops to about 8v. I am still using the two original yellow wires to feed the relay. But I did bypass the factory wiring plug. If you are still using that factory plug near the pass side valve cover, I would cut the yellow wires on either side of it and hook the yellow wires together directly. That plug gets melted from the glowplug feed wires, that might have been what you are smelling. And there are some other important smaller wires in that same plug. Keep the plug if you can for the small wires. I crimped 4 ring connectors on the yellow wires and bolted them together. It's handy to disconnect the wiring there when replacing the valve cover gasket or other work over there.

 

[franklin2]

P.S. Listening to some of the others on this board through the years, it sounds like Ford in the later models ditched the two yellow wires and went with one large wire. I do not see a problem with this as long as you route it carefully, since it will be hooked directly to the battery. If you get the voltage a little higher to the plugs, that can be a good thing. Since you have a manual button, you can control how long they are on, so I do not see a problem with them burning out. I am always a little conservative, glowing the plugs 5 seconds, then cranking, and then glowing 5 seconds again and then cranking again. You can experiment and see what works the best.

 

[rreegg]

If you can believe my dash gauge, when I glow my plugs on my 89, the dash gauge drops to about 8v.

Dang wonder if gauge is just typical ford dash gauge or if there’s some really hot wiring somewhere. My after market gauge shows about 10.5v while manually cycling GPs, the factory dash gauge is non-op. Thought that was even a bit low

 

[franklin2]

Dang wonder if gauge is just typical ford dash gauge or if there’s some really hot wiring somewhere. My after market gauge shows about 10.5v while manually cycling GPs, the factory dash gauge is non-op. Thought that was even a bit low

I do not know, but it works good and I watch that when I hit the button. That's how I know all the glowplugs are drawing power

 

[Clb]

I’d put it all back to stock. The stock system works very well and is easy to wire.

Til it's toast, yep.
What's your first impulse on the remaining stock harness issues he mentioned?