GM Service Manual Online
For 1990-2009 cars
Makes 🢒 Chevrolet 🢒 2004 🢒 C-Series Medium Duty Truck C6/7/8 - Mexico 🢒 Brakes 🢒 Antilock Brake System 🢒 Automatic Transmission Electronic Component Views
Figure 1:

Engine Harness to Engine (LG5), Left Side
Object Number: 689494 Size: MF
(1)C408/C409
(2)Upfitter TO PTO Connector
(3)Upfitter TRANS OPT Connector
(4)Powertrain Control Module (PCM) Connector
(5)Engine Oil Pressure (EOP) Switch
(6)Engine Oil Pressure (EOP) Gage Sensor
(7)Fuel Heater
Figure 2:

Automatic Transmission Harness --Typical-- without MTW/MX4/MWF
Object Number: 689497 Size: MF
(1)To Backup Lamp Switch
(2)Vehicle Speed Sensor (VSS)
(3)Automatic Transmission Modulator
(4)Neutral Safety Switch
(5)C408/C409
Figure 3:

Engine Harness to Transmission (MTW/MX4)
Object Number: 689982 Size: LF
(1)Turbine Shaft Speed (TSS) Sensor
(2)Automatic Transmission Connector
(3)Vehicle Speed Sensor (VSS)
(4)Park/Neutral Position (PNP) Switch
(5)Automatic Transmission Input Shaft Speed (ISS) Sensor
Figure 4:

Engine Harness to Transmission (MWF)
Object Number: 214808 Size: SF
(1)Transmission
(2)Automatic Transmission Input Shaft Speed (ISS) Sensor
(3)Vehicle Speed Sensor (VSS)
Figure 5:

Instrument Panel Harness to IP Mounted Components, Right Front View
Object Number: 689502 Size: MF
(1)Power Brake (P/B) Booster Pump Motor Relay
(2)Park Brake Pump Motor Relay
(3)Trailer Stop Lamp Relay
(4)Transmission Control Relay - MTW/MX4/Ignition Relay -- Engine Controls - L18
(5)ABS Relay Center
(6)Fuse Block 2 -- Underhood
(7)Fuse Block 1 -- Underhood
(8)C123
(9)C121
(10)Windshield Washer Fluid Pump
(11)Windshield Washer Reservoir
Figure 6:

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 7:

Automatic Transmission Shift Lever (Instrument Panel Mounted)
Object Number: 690222 Size: SF
(1)Automatic Transmission Shift Lever
(2)Convenience Center
Figure 8:

Inside of Left Frame Rail
Object Number: 690223 Size: SF
(1)Transmission Control Module (TCM) Interface Module
(2)Transmission Control Module (TCM)
Figure 1:

Transmission Control Module (M74)
Object Number: 769662 Size: MF
(1)Transmission Control Module Connectors
(2)Transmission Control Module
(3)Powertrain Control Module (PCM) (Gas) / Engine Control Module (ECM) (Diesel)
Figure 2:

Engine Harness to Transmission-Allison
Object Number: 769664 Size: MF
(1)Turbine Sensor Harness Connector
(2)Power Take-Off (PTO) Connector
(3)Output Speed Sensor Harness Connector
(4)Transfer Case Selector Shift Control Switch
(5)Transmission Connector Harness
(6)Park/Neutral Position (PNP) Switch Connectors
(7)Allison Transmission
(8)Engine Harness
(9)Automatic Transmission Input Shaft Speed (ISS) Sensor