If you have air brakes , with a floor mounted pedal , they should be directly under the floor from the pedal on the foot valve .
I had problems with mine , due to corrosion from water off the front wheel and the cruise control wouldn't work in the rain. Even the slightest amount of power conducted through the corrosion would tell the engine ECM to shut off the cruise. Before you replace the switches , I'd try a clean up of the switches and wiring and coat with a waterproof grease, that fixed mine and no problems for 4 years.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.