Re: 7.3 will not start.... Help
I had the same problem with my '99 F250 super duty with the same 7.3l turbo diesel. I replaced the starter relay on the fender wall and it didn't help. I replaced both batteries, still nothing. Finally replaced the altenator and that did the trick! No problems since installing new altenator. Test the out put of your altenator if you can get it running, sometimes it seems find but it takes a lot to crank these big engines. Mine had a short in it somewhere, that's why sometimes it would be fine then other times it would cause trouble just like you are describing. Best of luck, let us know how it turns out.