Hey Roost, Welcome to the site!
My 90 G30 also has an inop CC. The Brake fuse must be good, and there is a brake module on the Driver's side above the battery. Mine is faulty, and throwing a code. The FSM has a dizzying diagnostic array of what may be the cause.
The switch is a weak link, but you got that so....
Hope you have luck finding the fault. Good Wrenching!
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1990 Chevy G30 L19 7.4 EXT
Church Van, maternity division
DogVan
1988 Dodge B250
LA series 318 Wedge 5.2 TBI A500
Cabin Cruiser
'94 Dodge B350
www.xplorermotorhome.com/Xplorer MH model 230
230 hp LA series 360 Wedge MPI 5.9 A518 OD auto
Old vans are getting pricey!