GM Service Manual Online
For 1990-2009 cars only
Figure 1:

On the Steering Wheel/Column


Object Number: 826812  Size: LF
(1)Turn Signal/Multifunction Switch (Cruise Control ON/OFF, Resume/Accel and Set/Coast Switches (K34), Headlamp Dimmer Switch, Turn Signal Switch, Windshield Wiper and Windshield Washer Switches)
(2)Horn Switch Ground Contact
Figure 2:

Instrument Panel Switches, Center Forward View


Object Number: 1400889  Size: LF
(1)Outside Heated Mirror Switch (DNN)
(2)High Idle Switch (UF3) or Power Take-Off (PTO) Switch
(3)Exhaust Brake Switch (K40)
(4)Rear Axle Driver Control Switch - Two Speed (HPZ and Automatic Transmission)
(5)Traction Control Switch (NW9)
(6)Overdrive (OD) Defeat Switch (Allison® LCT)
(7)Marker Lamp Switch (JE4, RQ2 and U86, or JE4 and RQ3)