glow plug related

[02f350inpa]

have a 2002 f350 DRW that randomly doesnt want to kick in the GPR after sitting anywhere from 8-10 hr. to overnite(depending upon temp.)the question i have is could my EOT be bad and telling the PCM the motor is warm when it really isnt? little background-GPR and all 8 GP's new about 3 months ago and problem is kinda hit miss,1 time GPR will get energized fist try then other times you have to turn key multiple times before the GPR will kick in(know its being energized by watching test light hooked to GP side of GPR) in your opinion would you replace relay or EOT sensor(which is more likely the culprit),willing to replace both but would rather do 1 or the other

[countryraised]

hook your light up to the signal input side, if you are always getting input then it's the relay if it's hit and miss then look else where.