Been working through my 2002 Excursion 7.3 not starting. Garage kept, 55 degrees in my garage. Went out last week and truck wouldn't crank, all the lights on the dash came on, no dimming when I turned the key, but no engine cranking. Shifted thru the gears, no crank. Took a different car to work, came home and tried again, started right up and drove around. Next day, same thing, except she never came back to life, would not crank. Swapped starter relay under dash with backup lights relay and replaced the neutral safety switch with a new unit, no crank, but all dash lights look good. Had the starter tested, it tested ok, but they thought a terminal was about to break off, so I replaced the starter. With the new starter it cranked about 3 rotations, but then got dead battery symptoms (dash lights dimmed, clicking under dash). Load tested batteries, they failed and I replaced both batteries this morning with new group 65's and she turned over quick and fired right up. Success!! Drove it around the neighborhood for a few minutes and parked it back in the garage. Just went out to the X to go to work, and NO CRANK!! Dash lights look good and volt reader in cigarette lighter is showing appropriate readings. Ideas?

 

Alternator?

 

I was drawing 14.2 at idle, so I think alternator is running fine. Only drove the truck around for about 5 minutes with the new batteries, so I don't think they would have uncharged that quickly.