I can't specifically answer your question, but I can offer some advice:
Unless your 'new' tow vehicle is a 1970 International truck or something similar with a standard old-style hydraulic brake system, I'd leave the K-H in the old one when you sell it. To replace it, I'd opt for a new-style controller; either the computer-controlled inertial like the Tekonsha Prodigy (now being repackaged or copied in a number of brands) or the Jordan Ultima which is operated by a cable system attached to the brake pedal.
Tapping any late-model brake-line system is not a very good idea and has the potential of voiding the warranty, playing havoc with ABS, and doing who-knows-what-else to computer wheel sensors in the systems.
Most late-model tow vehicles are pre-wired for a controller, so they're a really easy install. Some vehicles now (although none yet that I know of that can tow anything) are even going to brake-by-wire instead of hydraulics at the pedal.
AIR 2053 Current: 2006 Born Free 32 RQ Kodiak Chassis, & 1995 Coachmen B-van
Former Airstreams: 1953 Flying Cloud, 1957 Overlander, 1961 Bambi, 1970 Safari Special, 1978 Argosy Minuet, 1985 325 Moho, 1994 Limited 34' Two-door, 1994 B190 "B-Van"