RPF PREMIUM MEMBER
Can we get confirmation on this that this is indeed Harrison Ford?
According to the commentary on the DVD, with Bob Gale and Neil Canton, the guy driving the jeep is Walter Scott, the stunt co-ordinator (I just listened to it). Could they have been wrong? Possibly. But they're the freaking Producers, and according to the commentary, they're the ones that hired him, so since there happens to be a close up of the jeep driver in the film, I would say they're probably correct in their identification. Mystery solved. And for the record, the guy looks nothing like Harrison Ford, so I get the feeling the OP didn't even check this one for accuracy.
Sort of related, wasn't Ford one of Elliots' teachers in ET? Or the principal? Scene was cut, of course, but I seem to remember that.