Truck won't start unless plugged in. When it's plugged in it starts right up. I replaced the GPR a couple months ago so I checked it with a multi meter and it was fine. I unplugged the UVC harness plugs and check the glow plug pins with a test light and I had one bad glow plug. I also had 1 UVC harness plug that the outside pins where burnt. So that gives me 3 glow plugs not working on the passenger side. I would think it would start with 5 glow plugs working. What else can I check? Sorry this is so long but I'm kind of stumped right now.