GMC 2003 C4C042 Owner's Manual page 338

Primary Underhood Fuse Block
Relay Usage
NOTE 1 LG4 Powertrain Control Valve,
L18/LB7 Fuel Pump,
LG5 Heated Fuel
IGN B Ignition
STARTER Starter
6-84
Relay Usage
HORN Horn
IGN A Ignition
PTO Power Take
REVERSE Reverse
NEUTRAL Neutral Start
START
Fuse Usage
RR DEFOG Rear Defog
ENG 1 Engine 1
ENG 3 Engine 3
-
PCM B Powertrain Control Module
BLANK Empty
ENG 4 Engine 4
ENG 2 Engine 2
HTD FUEL Heated Fuel
BLANK Empty
BLANK Empty
-
Off