Manual glow plug wiring issue

Hey guys. I have a 94 f250 with the 7.3idi n/a. Trucks been down for a month or two now. My glow plugs stopped heating a while back and I am attempting to get them to work so I can start the truck after replacing the fuel lines, filter, pump etc. I followed a guide on here to wire up a manual gp switch and I have an issue. When I turn the key to ON, the WTS light comes on and stays on without me pressing the switch and I am pretty sure the GPs are not heating as thd voltage never drops, whether I press the switch or not. I have triple checked the wiring, white wire run from relay to switch, blue wts wire attached to the same terminal as the white wire. I do not understand how this is possible unless the relay is fried internally and somehow delivering power to one terminal at all times but not to the GPs.

Sounds like you have it wired up wrong. There are a couple ways to wire these up.

I prefer to use a wire into the cab to the switch that has to be grounded. Safer that way - if the insulation rubs through then it will kill the glowplugs. But if you had it hot then if/when insulation rubs through you could have an electrical fire unless you use a fuse. Plus you potentially have to run two wires with the hot-method, one for the relay and one to 12V (unless you tap into 12v on the dash) - with ground the second wire is shorter (anything grounded will work)



So in this picture, if wiring it up my way, you would run the white wire from the relay ground into the cab to your switch. Relay input would get main power and another little wire connected here and ran to the relay signal post - providing power from the input side to the signal time. Relay output goes to the glow plugs. So to activate the relay and power the glowplugs you would then just hook the other side of your switch to a ground and push it. Don't use toggle switches, use a quality push button.

If you want WTS lights to still function, h ook up the stock WTS light wire to the relay output post. I don't recall where it is normally but if you do the wiring this way then it has to be on the relay output. If by accident you wire the WTS to relay ground should do nothing, and if you wire it to either relay signal or input it would be always on.



Alternatively, if you wanted to have your white wire to switch to be hot you would just switch a couple things: Add a fuse to the wire, doesn't need much since you are just triggering a relay . Relay input gets power from the batts. White wire goes to relay signal and button, with another wire to the switch being fed to 12V. WTS can be wired to either relay signal or relay output - output is still probably more useful as this will tell you if power is going through the relay. Relay ground gets hooked to the neg on battery or anywhere grounded. Relay output to glowplugs.

I will take a picture tomorrow and post it up. So that red wire is connected to the battery input and the relay signal post which would normally have received voltage from the ignition switch? The writeup I followed just puts a momentary switch on the ground wire but your setup seems to make much more sense as it rules out the ignition switch and turns the WTS light into a sort of tester to show you that it is sending signal to the gps.

ISPKI said:

I will take a picture tomorrow and post it up. So that red wire is connected to the battery input and the relay signal post which would normally have received voltage from the ignition switch? The writeup I followed just puts a momentary switch on the ground wire but your setup seems to make much more sense as it rules out the ignition switch and turns the WTS light into a sort of tester to show you that it is sending signal to the gps.

Click to expand...

Yes there is a red wire (doesn't have to be red ) that is about 3 inches long or so - just a small guy. One big loop crimped on one end and a little loop terminal crimped on the other so that power is provided from relay input (which is always hot) to the relay signal post. Then just run a wire directly from the ground post to the switch, then ground the other switchs' post. This bypasses the ignition switch entirely - I like to glow my plugs without having to have the keys in and in the run position. Yes using the WTS light on the relay output side will tell you if the relay is working. No light means either the light burnt out or your relay is bad or there is a problem with the wiring.

Originally (meaning the automated system) the ignition switch sent a signal to the glow plug controller, which sent a signal for several seconds to the relay signal post. There was another wire that came from the controller to turn on the WTS light. Real fun diagnosing something when every time to switch the key on and off it tries to glow 'em. And if one glowplug was dead the controller freaks out turning the relay on and off repeatedly. Multiple plugs out you'd get stranded. You can tell when they start failing with manual-pushbutton-control as it just takes a little longer to get started, starts rougher depending on how many are out and cleans up as it warms. But you won't get stranded near as easy too. I had an idea to test for glowplug health but that was with a custom harness...

You can also do all of this stuff similarly on the starter relay - same principles. I have two switches for the starter to help with diagnosing and whatnot. I have a switch right on the relay that is a toggle switch - if I ever need to be under the hood and cranking over I can do it alone now. And I have a pushbutton starter next to the glowplugs. The ford ignition system WILL break if you use the keys to crank the engine over. There is a cast piece of junk in the steering column that gives up after years and could leave you stranded if you don't know how to bypass it (and break the steering lock)...


Here is my switch panel on one side - the black one was a test run to see how I like it. Metal was too thin, I cut up an old computer case panel from a cheap computer... After I liked everything and the function a year or so later I used aluminum. The buttons are called bulgin switches, also known as vandal resistant switches. They are meant to be very reliable and durable. You can get momentary and toggle buttons in this type, although I strongly recommend momentary so someone else doesn't accidentally leave your plugs on.

The only thing I had to move was the tank selector switch. How often do you swap tanks, I bet less often than you start the truck up! I also removed the WTS light and put in another plate in place of it to switch off my stereo and tank selector switch. Some people sacrifice their change cubby but I like that space and the rest of those things were junk on here I use an LED for my "WTS" light, next to the glowplug button. The toggle switches are for fog light and reverse light, the reverse having a blinking LED to help prevent leaving them on accidentally

This is how mine is setup. White wire and blue WTS wire were connected bottom right. Top left is the Battery input. Top right had 3 large red wires (maybe 10 gauge?) two of which were crimped onto one ring terminal. The bottom right is output to GPs but has a yellow wire attached to it. My concern is that I do not know what the red wires go to. One must be to the ignition switch, but what are the two large red wires in the top right of the image? The two large red wires also have a green stripe on them.

See if this works.
https://drive.google.com/file/d/0B4bZOyQG0EUmeFRMemFoakg4Y2M/view?usp=docslist_api
Sent from my SAMSUNG-SM-G890A using Tapatalk

Thank you for the diagram. I just wired it up according to RHK's suggestion, I left the small red wire off the signal terminal thinking that was for the ignition but realized that is for the controller. Going to put the wire back on and see what happens.

There is something going on here, the WTS light does not turn on when I press the switch but I can hear the relay click. When I turn the ignition switch to "on" the WTS light comes on, and when I cranked it over, it pumped smoke out of the muffler and even coughed a little bit, still did not want to start.

Did you confirm that there is voltage to the terminals at the GPs while the manual switch is closed?

ISPKI said:

Thank you for the diagram. I just wired it up according to RHK's suggestion, I left the small red wire off the signal terminal thinking that was for the ignition but realized that is for the controller. Going to put the wire back on and see what happens.

There is something going on here, the WTS light does not turn on when I press the switch but I can hear the relay click. When I turn the ignition switch to "on" the WTS light comes on, and when I cranked it over, it pumped smoke out of the muffler and even coughed a little bit, still did not want to start.

Click to expand...

What color is the smoke - black and grey means some plugs are dead. All grey means all the plugs are dead or no power.

Are you trying to hook this up for pushbutton or use the controller? You can do both, but if you only want pushbutton then get all of the controller stuff out of there.

You should only have this combination: The big red wire with constant power to the input post, a small wire coming off the input post and the other end connected to signal OR hook the ignition wire here if you only want to be able to glow the plugs with your keys in the truck in the on position, a wire running to the switch in the cab is connected to the ground plug, and the output post is hooked to the WTS wire and the glowplugs.

Now the relay is labeled on there. I want to say the signal post is labeled S+?
The ground post looks like this almost always

Maybe you have the wiring mixed up. Sounds like you are using the red and green-stripe wire which is ignition-switch-power as I mentioned in this post above. I will draw up some pictures for you

Anytime you see a red wire with a green stripe, that is an ignition wire.

Either of these will work for you. Anything else might not but there are a few other ways to do it

Yes, I still have the red w/ green stripe wires hooked up because there are two of them and I was not sure where the second one went. I would like to eliminate the switch since mine is very worn out. I will pull the extra red wires off tomorrow and see what happens. Also need to test the gps for power, just have to figure out how to do that without a second person.

The smoke was all lighg greay, smelled like diesel, I am assuming because the plugs arent heating

Test the glow plugs: Get a test light, only a couple bucks or you can make one. One side has an alligator clip and it goes to the positive on battery or the positive on the relay would work. Then the other side looks like a screwdriver with a light and pointed chisel-tip sort of probe, poke it at the glow plug heads where the connectors attach. Light turns on - they *should* be good. no light means they are definitely bad.

Glowplugs are sort've like lightbulbs - when they work power flows through them, when they burn out it doesn't. Same principle, but some glowplugs will only partially fail so if they all light up they could just we wore out but not fully burnt out. If one fails you could swap just it out, but its probably better to swap them all. If you dont know what kind of glowplugs you have then you should pull them, some brands would have the tips fail and break off into the cylinder.

Grey smoke is bad glowplugs or they aren't being powered up. Try taking everything off the relay, then hooking it up like I described.

The GPs are brand new motorcraft plugs, maybe 150miles on them. I just pulled the two red wires off and moved the position of the WTS light. I had it bolted to the end of the squiggly band resistor thing where the GP wires are attached, rather than the relay side. The WTS light now comes on only when I press the momentary switch. I also measured voltage on a few of the GPs and confirmed that I am getting power to them. Now I just need to charge the batteries and see if she will fire up.

Good luck