Do you dash HVAC controls work? Try switching from defrost to say feet or dash vents. This will confirm you've got vacuum in the lines or not. From there the I would suggest you've got power at the unit(by the engine) then the brake switch, then....maybe confirm the wheel control signal is making it back.
FWIW I replaced that POS vacuum pump(once I finally got the damn thing out) with a vacuum pump from Summit. Thing was around $90 and the size of a windshield washer pump. It's worked great from Ca to AK and now on my way back down.
1994 Fleetwood Southwind 36AD, 5.9 cummins(300+hp), Allison-3060 6spd. Oshkosh Chassis. 1999 Honda CR-V toad...Retired Coast Guard CWO.