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

Relays-Lower Exterior Bulkhead, Right Side


Object Number: 689999  Size: MF
(1)Automatic Transmission Modulator Relay
(2)Starter Relay
(3)Engine Brake Relay (LG5/K40)
(4)Bulkhead
Figure 2:

Instrument Panel, Left View


Object Number: 690018  Size: SF
(1)Trailer Marker Lamp Switch
(2)Outside Heated Mirror Switch
(3)Exhaust Brake Switch
Figure 3:

Frame Crossmember, Rear of Cab


Object Number: 690020  Size: SF
(1)Engine Brake Actuator Control Valve