This has probably already been answered somewhere, but when I search the results are nothing to do with the specific issue I am having. Truck is a 1984 F-250 with the 6.9 IDI and manual transmission. Only modifications are aftermarket air cleaner, slightly advanced timing, and a momentary switch to replace the factory glow plug controller. The issue I am having is that the glow plugs keep burning out. When I bought the truck it had new glow plugs in it, and after a few months those burned out. I replaced them with Motorcraft ZD1A glow plugs, and after about a month those burned out as well. I hold the momentary switch down for a maximum of 10 seconds at a time, and a couple of times the glow plug light on the dash stayed on after the momentary switch was released, a couple times for upwards of 20-30 seconds. This is leading me to think that the relay wired into the momentary switch is sticking, but was curious if anyone has had a similar experience, or any advice. Thanks in advance!