I worked on the 7.3 for U-Haul for 2 years and found the best is to use the controller from International and the International glow plugs. We had a 94 E-350 service truck with the 7.3 in Washington State and this is what we used for over two years with no failure. My question is are you letting the controller run a full cycle or are you cranking during the cycle. If it is short cycling you may have a damaged wiring harness. Trying to start during the cycle shortens the life of the controllers.

 

I've installed the manual push button on 4 different Trucks. But I simply wired directly to the glow plug solenoid on the RH fender well eliminating the controller and saveing over a 100 bones. Its a good idea to replace the solenoid. On one occasion the solenoid contacts welded themselves together and effectivly burnt up all 8 glow plugs 2 days after the push button was installed. To help reduce smokeing after start up, manually cycle the push button on 2-3 seconds and off 2-3 seconds.

 

Are you sure about that solenoid on the right side?? I distinctly remember that as just a signal from the ignition switch to the starter solenoid (similar to early ford with no solenoid on the starter}. Ford utilized this system with the Hitachi starters. The only Glow Plug Solenoid is on the controler. The controler works by producing a temperature signal depending on the resitance from glow plugs themselves. Normal cycle time is 25-45 seconds 65 down to 32 degrees faranhiet. At that time 3 to 5 loud clicks should be heard from the controller. If you have the light installed you should have it come on when the controller is energised and go out when it is through you then have approximately 60 seconds to start. If this fails after two tries then cycle the glow plugs again. I spent many a cold and wet night in the Cascades and Northern Washington replacing starting system components (starters, controlers, solenoids, glow plugs, cables, wiring harnesses} due to pepole failing to let the sytem do its thing. I do not like replacing factory designed components as a certified mechanic but if adding a seperate switch then mount a standard
Ford starter solenoid to a solid ground, use a heavy gauge wire (preferably a fusable link) directly from the positive side of the battery to the battery side of the solinoid and from the starter side to the glow plug wiring. connect the power from your switch to the S terminal (do not utilize the I terminal) and cycle 10 seconds on 5 seconds off at least twice and on a really cold morning 4 times and it should fire right up. Additional hard starting problems on these engines is caused by the little bitty check valve in the filter vent hose. On the top of the filter housing is a small brass fiting that a 1/8 or 1/4 rubber hose connects to. If the engine fires and dies after a very short run and requires several reattempts to start this fitting has failed. To verify remove the fitting blow frothe threaded end(by mouth) then look through it. If you see daylight then the little rubber duck bill has failed. I don't know if Ford carries these but I know International does.

 

On the 6.9 83 - 86 the glow plug relay was on the inner fender well right behind the battery.
On the 87 6.9 and the 7.3 IDI motors till 94 the relay was on the rear of the engine intake manifold on top of the controller.

 

I have never seen just a relay for the glow plugs. The only relays I have seen for the glow plugs is part of the controler. The relay you are describing still sounds like the starter relay. It wouldn't be the first time I've mixed up the info though. Before modifing any thing like this be extra sure and verify with the wiring diagrams and the manuals what is what.

 

Eric, your 86 and all the 6.9s except the last year have a relay on the passenger fender behind the battery, if it hasn't fallen off it has a cap that says do not jump start here. The glow plug controller is on the back of the left head but all it sends is a signal voltage to this relay which actually works the plugs.

I have found it quite painless to convert this 6.9 system to the 7.3 system with minimal wiring modification. The new controller (with relay) goes where the old controller was.

Birken

 

Aside from the Contoller, on the right side behind the battery is 2 relays. one mounted to the inside of the fender, just below the hood line is the Starter relay.
Below that on the fender liner is what looks like another starter relay. But it isn't, it's the Timer relay for the Glow plugs, and also on that side in front of the battery is another Glow plug relay. But this one looks like a relay type can.

 

I posted a picture of the glow plug relay for the 6.9 which is located behind the battery passenger's side.
Saigon

 

Dave knows what I'm talking about. The starter solenoid is up on the side of the fender and the glow plug solenoid is mounted on the fender well behind the battery for the 86 and older diesels.

But anyway, all I know is what I got is simple and works.