I have an '89 F350, 7.3L diesel. I have trouble getting it started when engine is cold. I've checked the glow-plugs and replaced all the bad ones, I've replaced the glow-plug relay/sensor combination unit. When I turn the ign. Switch on, the "wait" light stays on for just a second or two, then you can here the control unit click about every second, for approx. 20 seconds. Once the engine warms up even a little it will start right up.
