Since the SMI Air Force One part # SM99243 is designed for tow vehicles that have air brakes the air hose connects to the air brake system and is what tells the unit installed on the towed vehicle how much braking pressure needs to be applied. Basically it connects at the rear of the motorhome and then to the front of the towed vehicle. I attached a diagram of the whole setup that shows the air hose you mentioned pointed out. view full answer...
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