i have a 1991 for e-350 van, it has a 7.3l motor. i am having some problems with the glow plug circuit. when i turn the truck on the wait to start light will only come on for a second at most and then turn off, the truck is also almost impossible to start unless the block heater is hooked up for 30 or so min. I live in cali and it is not -30 degrees out side which is leading me to think that my glow plug circuit is not working or staying on. i also can hear a loud clicking noise coming from the solinoid ( or what ever the thing is called that all the glow plugs tie into mounted rite above the tranny with the plastic cover on it. it doesn't do it everytime but it does do it oftenly and it seems to click for around 10 seconds after i turn the key on and then shuts off. do you guys have any idea what could be going wrong or if you could point me in the right direction?  

i am experiencing similar problems with my 2003 7.3l motor.  from what i've read the lenght of time light comes on is not relevant to working condition of the glow plug circuit.  when it got chilly outside, i'd have to plug up the truck or it would not start.  as long as i plugged up the truck it would start.  as far as replacing the glow plugs goes, i'd rather plug the truck in than go through that expense... i bought a heavy duty plug timer from lowes an plugged it in with a heavy duty outdoor extension cord and set the timer to come on 1 hour before i go to work...it works well.  

diesel-kevin try replacing your glow plug relay