On 2000 7.3 will not start below 30 degrees if not pluged in. I have replaced glow plugs and still same issues.Now i am trying to find the real problem before wasting more time and money.there are two relays there. one seems to go to intake, is this a heat element also? I assume the other is glow plugs? I have tried testing both and they test the same. I have 12 v on large stud comming in and two small studs on each test 12 v all the time also.The large stud i think goes to gp and intake i test 0 v all the time even when key is first turned on and engine is cold 40 degrees.

 

eBay Guides - Ford diesel glow plug relay trouble shooting this has quite of good info see if it will help with your problem

 

you should have two relays, one on the passenger fender and one on top of the motor next to the fuel filter/bowl. the one on the motor is the one for you gp's, your relay is most likely bad so just buy one for 40$. that should be your fix, there are no intake heater elements on powerstrokes.

 

ok thanks
guys