This has been discussed before, but i can't find where it has been unified, so:
VMM Inputs are (mostly) computer signal inputs, i.e. the labeled white wire out from the VMM is a computer voltage looking for ground. When ground is contacted, the signal indicated to "activate" the applicable function(s).
E.g. Driving Light Switch connects an input to Ground, which tells the VMM computer to send voltage on an Output line to the driving lights. Outputs are auto-resetting breakered lines, most are good for 6A at 12V.
On the Inputs, if you add so much as a relay coil load (<0.2A) to the ground seeking signal, you will over time fry the Input circuit in the VMM. This is a costly mistake. If you get a replacement VMM, its $1,500 for the part & then the labor bill on top. The subject comes up since I'm talking to the second coach owner in a few years to have this happen; she of course had no idea, and probably had a shop do the work to install a brake controller off a relay powered by the brake light Input circuit, and now has no brake lights (which are necessary for brake lights, CC Off signal, and Aux Brake Boost signal that I recall, might be other things powered off brake light signal also that I can't recall).
Good new is- most of these single circuit snafu's can be rectified by taking the signal analog. For my Driving Light switch signal, which came pre-burnt out in my rug, I snipped off the Input & Output wires off the front VMM, tapped new 12V at the large studs at bulkhead, and ran a relay coil to the Switch (still looking for Ground as that was a simple way to leave the wiring the way it was) to power the Output.
For burnt out Brake Light signal its more complicated, but only a matter of hunting down the full compliment of Outputs affected. CC Off is handled by the SmartWheel module, which is also used on Monaco's but in an analog fashion; Aux Brake Boost goes out to the fat relay above the master cylinder and requires power in KeyOff and in KeyON-EngineOff modes so probably two relays new req'd, and of course you have to get power to the brake lights. There is a Rear VMM Output called Brake Signal, which may be to ECM to signal Cancel CC, or it might be to someplace else; if doing this you will have to ascertain what that is & how it operates. Using relays to do the decision making avoids the hefty VMM replacement cost for just one circuit, and will get you on the road faster. For Brake Light signal, the SmartWheel module needs to be reconfigured for analog input and then U need to arrange the appropriate input (see Troubleshooting Guide for SmartWheel on ACA Tech Library
If you want to add a trailer brake controller to a Vansco equipped coach, there are threads here on the Alpine forum; use the Search features for full details, e.g. like this thread