Paul you be a Ford Man I be a Ford Man ..I not trust them
O.k. Guys this is what I found ..there are 2 relays on the top of the Motor mounted front to back
The rear is the Glow Plug Relay. The large post with the rubber cover is a full time 12V the Other Large Post goes to the Glow Plugs...the Little Wire Near the rear Is where when you turn the key over ic hot closing the contacts putting power to the Plugs....I'm not sure what the front is for I don't think it is a ground but I never got any power from it???
The Front relay is for the intake air heater that's in the wye pipe at the outlet of the turbo (just behind the vacuum relay with the red and green tubing in your photo). I don't remember right now how it's controlled, but it turns on during warm up idle to help cut down on the white smoke.
If it goes bad, it will just put out more white smoke than usual because the intake air isn't being preheated.
Hope this help..