Crank but intermittent start of F150
My truck will start fine for a long time and then all of the sudden it won't. I was told to switch relays, which I did, and it would start, and it did until yesterday. After towing to Ford Dealership they were working on it and out of the blue it started. They said b/c it started they can't find anything wrong to check. Worried this could happen anytime in the future and I would be stranded. Any suggestions? HELP