Ford 7.3 relay module

Check the resistance of all 8 glow plugs. It only takes one bad one for the relay to work improperly. The module uses the impedance of the glow plugs to determine glow plug on-time.

Hi Doug, Wow a classic. 92' should be a pre turbo model unless it had a turbo added on. These have a glow plug module mounted at the top rear center of the intake, it has a cover over it. It also has a coolant temp electric switch on the front passenger head for the GP module. That switch typically goes bad with age. That switch is what activates the module when the key is turned on. That…

Ahh, I was wondering what that switch was SOL (Smiling Out Loud). That makes sense with the CTS activating the ground control…. I don't mean to doubt your understanding of how it works but here is what the service information says. “The glow plug controller determines the glow plug temperature by electronically measuring the resistance of the glow plugs,… A ‘Wait To Start’ lamp on the…

Well that didn't seem to work. I purchased a new module and going to hook it up tomorrow and see if that fixes it. If not we'll go from there. And I know I know I tried my best not to be a parts changer but nothing else worked. 😒

That glow plug system is a stand alone system that uses the resistance of the glow plugs to calculate the on time of the glow plugs. Take a look at the wiring diagram. diag​.​net/file/fy6s924aj… ​ If you are experiencing the problem of the glow plugs not staying on long enough, you will notice the GP relay will rapidly click on and off. This is caused by one or more of the glow…

Yeah I figured that out. Looks like to me that this diagram shows that if the wait to start light bulb in the dash is burnt out, like Glenn said, it's not going to properly activate the module relay. So it looks like I have to get in the dash to check the bulb & the new module wouldn't work either.

Hi Doug, You may not see one of these again for a long time, but you will remember they can be a challenge. As Albin indicated, go with Motorcraft if at all possible. Geek Auto and Rock Auto are usually good sources, even Ebay surprises me from time to time with OE new parts. When it comes to the bulb(s), use quality HD ones like Sylvania. For the temp switch, I was recalling the earlier 6.9…

Doug, That temp switch does not control the glow plugs. They are controlled only by their collective resistance. That switch is for timing advance and fast idle. Replacing 1 or 2 is usually a waste of time, do them all. Use only Ford/Motorcraft! You've been warned.

Some of those old coked up glow plugs are pretty hard to get out. Those like to swell and coke pretty badly if I remember. I always unscrewed them until the thread were free and then put a vacuum line or fuel line over the plug and put it in a drill and spun it while tapping the glow Plug back towards the Threads and the cooking grinds off that way and you can pull them right out.

You can also start the engine up and unscrew it and let the compression do all the hard work.

Make sure the grond connection on the block that the controller connects to is clean and there are good grounds from the block to the batts. That conroller is fussy about it's ground. It should still cycle on even with several bad plugs. For testing glow plugs I have alway used an incandescent bulb test light. Hook the test light lead to the pos batt post. Touch the tip of the glow plug to the…

Hi Doug, Newer 7.3 in 94.5 and up were a Power Stroke and they are a different animal to learn about. I worked for a few years on early 6.9 and 7.3 none-turbo diesels, and it was a definite learning curve with the newer ones. Glad you got this one resolved.