So first off hello I'm from central MN and just picked up my first 1983 M939A1 five ton beast from Camp Ripley MN I love this truck and only had it a week but the diff locks won't engage when I flip the switch or when I put it in low range could it be junk in the air line? Also the windshield whippers won't operate at all and the horn clicks but no air goes threw? I do live in Minnesota so could it be possible that ice is in the lines or does this sound weird to anyone? Oh and I need a block heater for it but don't know where to start looking it has a cummins 250 cnh motor thanks for now guys the pic on my profile is the new truck