I got really lucky and picked one up today from an old friend that works on Amps, Speakers and Decks. Someone didn't pay the bill, and I got an Orion MBR 70 for $50. Sadly, I thought they had a (-) hook up for the batteries, but to my amazement it was (+) and (-) for the Unit power, and only Output for Front and Rear battery with the (+) Symbol.
Here is my question, Do you only hook the (+) to each battery?? Do you ground the Unit Chasis or just the Electronic power on ground? Surely with someone here has a diagram.
Tell me your email address and I'll send you a copy of the manual when I find it. It's quite easy to hook up. I have one in my car. You also lucked out on the unit. They normally sell over $150 or isn't available.