I have found that all four of the glow plugs on the drivers side of my 6.5 are failed while all four on the passenger side are good. All eight were replaced at the same time about three years ago. Does anyone know if there could be a reason for this or just coincidence? Is there some other part (controller) or other that could cause all on one side to fail?

Thanks.

Each bank is tied to the same terminal on the controller, disconnect there and put an ampmeter in series with the leads to each bank. you should read 60 amps on each lead. A bad connection or hi resistence lead would cause low output or no output, on passenger side making them last longer. What glows are you using? The delco 60g,s seem to last for me, but I have to extend the run time below 40 degrees F There are many reports here on some brands of plugs failing. at least the drivers side is easier to swap out!

The glow plugs just taken out were WAP plugs 6A834G050. Original plugs that were in until three years ago were AC11G's. I just replaced the WAP's with Autolite 1110's today. Haven't started it up yet as I also have a fuel tank problem unresolved and out of the truck. Figured I make some other maintenance checks while dealing with the tank and found the plug issue. What do you think of the Autolites?

I believe there is a fusable link on each side too that can cause one side to fail while the other side is still working.

Honestly, this forum has not had good experience with WAP. There was a thread a few years ago about it being failing prematurely after only less than 1 year of service especially in the cold weather locations.

The Autolite will definitely better than WAP. From what I heard, it is similar to AC 11G. There is not too much experience with Autolite. The ones that have the best experience are AC 60G and Bosch Duraterms. A lot of people in this forum have used them and have good experience with them.