I believe that for a general rule they fuse a circuit for about 50% more than the expected use, so I bet your wiper circuit would'nt pull more than 10 amps at best. I think we have a pretty good ballpark estimate of what they'll pull, then.
I'd bet the 7 of the Summit could be matched by the low speed of the wiper motor. No use spending the $250-plus for that, huh!