I put it down to a dead cell in the start battery. It showed good voltage on a multi meter but wasn't going to leave any stone unturned so put the load tester on it and it wasn't good. Got a new battery under warranty and all was good after that.
2 weeks later I removed the brake light switch and seen some carbon like stuff on the points so I got a brake light switch from the local ford dealer for under $20 so changed it as well.
I haven't had it come back since.
Cheers Ean

