Originally Posted by CampSpringsJohn

If the glow plugs are bad, you replace all of them at the same time. As for jumping the relay, do what I said above first. If the light does not dim like I said, then you have either a glow plug relay not working, or the glow plugs are bad. If the light does not dim, find the glow plug relay. Take a screwdriver (an old one that you don't care if it gets burn marks on it) and cross the main terminals with it. What you are doing is completing the circuit and bypassing the glow plug relay. Keep the terminals crossed with the screwdriver for about 30 seconds or so, (the screwdriver will get very hot) then go start your truck. If it fires right up, you've found your problem. When you change the glow plug relay, you need to make sure it has good contact where it bolts up to the bracket.