Kenworth Schematic help needed..no jakes

I have a 98 KW w900L in the shopw with 1lw Cat 3406e...no jakes....has smart wheel...they have replaced vip smart wheel module......cruise works....lights flash works....jake buttons illuminate when depressed....but jakes do not come on......looking at ecm read out with ET....clutch and brake switch are working correct....but engine retarder always shows disabled...even when switches are on ...need schematics for smart wheel....for kenworth....and maybe even cat....have checked all fuses and relays I can find...thanks 704-507-2453 cell 704-888-2093 shop