Glow Plug Help

[Bio-Bradley]

Calling all 7.3 idi experts, shade tree mechanics and enthusiasts...

I've got an 89 ford f350 7.3 idi. It's got an aftermarket glow plug solenoid/relay. This system is installed as follows: purple wire goes from +battery terminal to the push button switch on dash(now there is an inline fuse here where there was not one before) (see pic IMG_0295). There is another purple wire that goes from the push button switch to the glow plug solenoid (S terminal). One of the solenoid terminals house the yellow wires coming from the +terminal on the starter solenoid and the opposing terminal has the orange wires that go to the glow plugs. (see pic IMG_0298 & IMG_0299). Pic IMG_0299 show the red factory wire and blue wire for WTS light disconnected and terminated. The solenoid I removed looks identical to the new ones. Unfortunately it was brittle and broke apart when loosening the nuts on the larger terminals so I can't use it anymore.

The problem: Originally I was noticing fluctuating voltage on my voltmeter (location is A-pillar) when I press the glow plug button. It used to be consistent. I've installed 3 different new solenoids thinking the solenoid was the issue. Two from Standard (RY175) and one from NAPA (GPR200) rated for diesel 89 ford f350 7.3 idi glow plug solenoid. With each installation, there is no longer a voltage drop registering on the volmeter and the glow plugs no longer heat up. I have tested each glow plug using a light-up circuit tester by attaching to the +terminal on the battery & to the top of the unplugged glow plug. The light turns on when I make contact on all 8. I've done the same with the 8 wiring caps that attach to the glow plugs showing the same result of the light coming on. I have replaced the push button glow plug activator on the dash as well. Electrical work is not my strong suit. I have installed the glow plug solenoid just as the old one was installed. Now, when I push the glow plug button under the dash, I no longer get a voltage drop and the glow plugs don't heat up. ***. BTW, I can start the truck after the block heater has been plugged in for a few hours. Weather today in Washington is 75F & sunny. Truck is parked in the garage.

Have I wired it wrong? Should I wire it differently? Other test options to help isolate the issue? It seems to me that the solenoid is not getting the power it needs to activate allowing the stronger amperage to flow to the glow plugs. Thoughts? Any and all advice is welcome!! Thanks in advance for your perspectives.

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[bbjordan]

You need a ground wire on the other small terminal on the solenoid.

 

[Bio-Bradley]

You need a ground wire on the other small terminal on the solenoid.

Thanks bbjordan. I wondered that, but the previous solenoid didn't have that. Based on my web research, it seems that some solenoids are grounded through the base plate and others are not. How would I know which is which? The new ones don't come with paperwork or wiring diagrams.

 

[franklin2]

Get a voltmeter and put it on ohms, rx1. Touch the meter leads together, it should read close to zero ohms. Then unplug the small wire off the solenoid and touch one meter lead to that one small terminal, and the other meter lead to the baseplate. If you get no reading on the meter, keep the one lead on the small terminal and move the other lead from the baseplate to the other small terminal. If you get a reading, you need a short ground wire going to that other small terminal to make it work.

The meter is reading through the coil windings in the solenoid. No reading means no connection to the solenoid coil.

 

[Thewespaul]

If you look at how these are triggered in the factory setup, the relay gets 12v from ignition, and the solid stay controller feeds a ground in to close the contacts. So any time the truck is running the relay is powered.

 

[Bio-Bradley]

Get a voltmeter and put it on ohms, rx1. Touch the meter leads together, it should read close to zero ohms. Then unplug the small wire off the solenoid and touch one meter lead to that one small terminal, and the other meter lead to the baseplate. If you get no reading on the meter, keep the one lead on the small terminal and move the other lead from the baseplate to the other small terminal. If you get a reading, you need a short ground wire going to that other small terminal to make it work.

I did the testing as you advised and it needed to be grounded. Thanks! Appreciate the help.

 

[bbjordan]

I'm not aware if you can tell if it's grounded internally, but if in doubt, check it out.

Question is: did it work? Did you start the engine with the glow plugs?

 

[Bio-Bradley]

Question is: did it work? Did you start the engine with the glow plugs?

Sorry. Yes! It worked and I got it started with the glow plugs. Thanks a million!