If you have a battery on the tongue, then running two wires directly from the jack to the battery is OK, because both wires would be short. But in a 2720 SL, the battery is a long ways away, and you need long wires to reach it. And long wires cause a bit of voltage drop because of their resistance. You don't have a lot of choice about running a long wire to the positive side of the battery. But you can eliminate the long wire to the negative side of the battery by using the trailer frame as the connection. The frame, being a big hunk of steel, has much less resistance than a wire, and hence less voltage drop. And less voltage drop means more voltage available to run the jack. The only challenge to using the frame is that you have to bridge the gap between the jack and the actual frame of the trailer - the swing point of the swing tongue is a lousy conductor.
Besides, it saves the cost of 25 feet of wire!
Bill
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