GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC C Pickup - 2WD (CNG) 🢒 Engine 🢒 Engine Controls - 5.0L and 5.7L 🢒 Engine Controls Component Views
Figure 1:

Underhood Fuse/Relay Center (1998 Only)
Object Number: 318669 Size: MF
(1)Aux B
(2)Aux A
(3)Aux B (30 amp)
(4)Lighting (50 amp)
(5)Aux A (30 amp)
(6)Battery (50 amp)
(7)Spare (10 amp)
(8)Fuse puller
(9)Spare (20 amp)
(10)Spare (30 amp)
(11)Ignition A (40 amp)
(12)ECM B (20 amp)
(13)Horn (20 amp)
(14)Air conditioning (10 amp)
(15)Ignition B (50 amp)
(16)Rear defog (30 amp)
(17)Aux fan (30 amp)
(18)ABS (60 amp)
(19)Ignition E (10 amp)
(20)ECM 1 (20 amp)
(21)Engine 1 (20 amp)
(22)Blower (50 amp)
(23)CNG (20 amp)
(24)Stop/Hazard (30 amp)
(25)Not Used
(26)Diode 1
(27)Diode 2
(28)Horn relay
(29)Fuel pump relay
(30)A/C relay
(31)A.I.R. relay
(32)Starter relay
(33)Brake lamp relay
(34)Heated seats/CNG (40 amp)
Figure 2:

Alternative Fuels Engine Control Unit (AF ECU)
Object Number: 296416 Size: SH
(1)AF ECU
(2)AF ECU Connector -- C003 Clear
(3)AF ECU Connector -- C002 Red
(4)AF ECU Connector -- C001 Blue
Figure 3:

Alternative Fuels (AF) Underhood Fuse/Relay Center (1997)
Object Number: 296411 Size: SH
(1)Fuel Pump Relay
(2)Fuse 1 20 amp (Power)
(3)Fuel Gauge Relay
(4)Fuse 2 10 amp (Ignition)
(5)Lock-off Relay
(6)Ignition Relay
Figure 4:

Alternative Fuels (AF) Underhood Fuse/Relay Center (1998)
Object Number: 296413 Size: SH
(1)Fuel Pump Relay
(2)Fuel Gauge Relay
(3)Lock-off Relay
(4)Ignition Relay
Figure 5:

Fuel Sending Unit and High Pressure Lock-Off (1997 Only)
Object Number: 296428 Size: SH
(1)High Pressure Lock-off (HPL) Connector - C313
(2)Fuel Sending Unit (FSU) Connector - C315
Figure 6:

Fuel Sending Unit and High Pressure Lock-Off (1998 Only)
Object Number: 296397 Size: SH
(1)HPL Connector -- C313 Black
(2)FTS Connector -- C316 White
(3)FPS Connector -- C315 Black
Figure 7:

Gas Mass Sensor/Mixture Control Valve
Object Number: 296415 Size: SH
(1)GMS/MCV
(2)MCV Connector -- C021 Black
(3)GMS Connector -- C010 Black
(4)LPL Connector -- C014 Black
(5)LPL
Figure 8:

In-Line Engine Harness Connectors
Object Number: 296418 Size: SH
(1)10-Way In-Line Connector -- C017 Gray
(2)10-Way In-Line Connector -- C018 Black
(3)6-Way In-Line Connector -- C019 Black (1998 Only)
Figure 9:

Instrument Panel Connections
Object Number: 296430 Size: SH
(1)Cargo Lamp Switch Connector -- C212 Black
(2)Fuel Gauge Selector Switch/Fuel Indicator Lamp Connector -- C239 Gray
Figure 10:

IP and Rear Lamp Connectors (1997 Only)
Object Number: 296419 Size: SH
(1)In-Line Engine Harness Connector - C103 Gray (1997 Only)
(2)In-Line IP Harness Connector - C104 Gray (1997 Only)
Figure 11:

Wire Harness Ground Connection
Object Number: 296421 Size: SH
(1)Engine Ground -- G103