Starting Problems

I have a 1992 f 350 with the 7.3 idi. The old glow plugs on my truck burnt out so I took out the 6 volt glow plugs with 12 volt glow plugs so they will not burn out. I also took out the relay and timer and put a continuous duty sylonoid in to replace them and a switch in the dash to run the glow plugs. Once I installed all of this I tried to start it to test the glow plugs I cycled them for 45 seconds and tried to start it and it turned over but never tried to start it just kept turning over. I tried it a few more times and the same thing happened so I let it sit over night and the next day my dad tried it. He cycled them for about 30 seconds and it didnt start so he tried it one more time after cycling them again and it started. He said it started really rough like one cylinder started at a time. That is the only time it has started since. It acts like it is not getting fuel to ignite to start and I dont know why it would act like it is now. Any ideas on what to try or test to see how to start it?