I hope this answers all and a bit more..
First Tully, there are adapters that are readily available to go from one plug type to another. Another solution might be to just change the trailer plug. It is easy to make the change with a simple multi-tester. The electric brakes work off of the same connection if the trailer brakes are electric. Your friend probably had surge brakes that activate when the tow vehicle activates it's brakes, (such as in JAKE BRAKE) If the trailer has electric brakes you will need to have a brake activator installed. This could require some extensive wiring, depending on the type of activator installed. Having your trailer brakes applied is good when you apply ANY brake on the tow vehicle. You need to check (multi-tester time again) to see if the bus plug has 12 or 24v. My bet is that it has 12V if factory installed. My '97 CC has factory wired 12V.
Let us know if you have any more questions Tully. Good Luck!!!
Darl