Seen it before, last year in fact this van had a new alt/starter/battery, but would do nothing or clunk like a flat battery even though it wasn't.
I found the problem on this one to be a high resistance on the solenoid feed wire, specifically the terminal on the end that bolts to the solenoid, I cut this off and resoldered another one(gold plated) on, it then started when covered in snow after being left weeks and weeks, the oe crimp is crap on the ford terminal, the solenoid draws momentarily 10 amps when in engagement.
Might be worth a look.
tabetha