Thanks and what's that black box

[Rdquest]

First, I want to thank the people who responded to my first ever post regarding my roof billowing while parked. My second post pertains to a little black box I found in one of the outside storage compartments. It appears to be original to the MH (class c four winds 1997). It is about 12 inches by 12 inches by 6 inches and just barely fits into the small storage compartment. I stuck my hand in there to get a pix but it's close quarters and not much to see but a yellow sticker on the front of the box stating " CAUTION. THIS SIDE UP. The compressor unit may be mounted in a horizontal position, however when mounting the compressor in a vertical position, this end must point upward. Mounting the compressor in any other way will prevent moisture from draining out the petcock. This moisture can result in non warranty compressor failure. In addition, the moisture can freeze in the braking system causing the brakes to lock up on the towed vehicle (not covered by warranty. Mount this compressor unit in an area that is clean, dry and ventilated and protected. Failure to comply can result in compressor failure, property damage and personal injury."
So what does this compressor do??? It has a red drain tube that hangs out below the belly of the MH. It has some wires coming out of it. It is not reachable to open the box or use it for any secondary purpose that I can see. My husband is a truck mechanic and he can not figure out what it is. He says it must be something they used years ago on MH's and not now. Can anyone tell us the purpose of this 'black box'???? BY the way, the MH has the usual brake box and plug installed to tow with.

[Isaac-1]

Sounds like an air compressor operated Towed car braking system, though I don't know which one.

[Rdquest]

Well y'all it was a supplemental brake for the towed vehicle. It appears to be original and non functional since the parts that hook to the towed vehicle are missing. Brakemaster 9000 is what it is. Boy these MH manufacturers make it difficult to obtain info on older used RVs.