GMC Forward Control P3500 (1985-1999) yel Wiring diagrams

BLK WIRE BLU WIRE BRAKE SWITCH (ON BRAKE PEDAL SUPPORT) BRN WIRE DK BLU WIRE DK GRN WIRE FUSE BLOCK- I/P GRN WIRE HAZARD HAZARD FLASHER (RIGHT SIDE OF STEERING COLUMN) HEAD HEADLIGHT SWITCH HOT AT ALL TIMES HOT IN RUN, BULB TEST OR START I/P DIMMER SWITCH INSTRUMENT CLUSTER LEFT FRONT MARKER LAMP LEFT LICENSE LAMP LEFT TAIL/STOP TURN LAMP LEFT TURN INDICATOR LT BLU WIRE LT GRN WIRE LT LT NORMAL OFF ORG/ WIRE PARK PPL PROVISIONS FOR PARK LAMPS PROVISIONS FOR REAR MARKER LAMPS RIGHT BACKUP LAMP LEFT BACKUP LAMP RIGHT FRONT MARKER LAMP RIGHT FRONT PARK/ TURN LAMP LEFT FRONT PARK/ TURN LAMP RIGHT LICENSE LAMP RIGHT TAIL/STOP/ TURN LAMP RIGHT TURN INDICATOR STOP/ HAZ FUSE TAIL LPS FUSE TURN LEFT TURN RIGHT TURN SIGNAL FLASHER TURN-B/U FUSE TURN/HAZARD SWITCH (LEFT SIDE OF STEERING COLUMN) WHT WIRE YEL WIRE

BACKUP LAMP SWITCH (ON STEERING COLUMN) BLK WIRE BLU WIRE BRN WIRE DK BLU WIRE DK GRN WIRE FUSE BLOCK (BEHIND LEFT SIDE OF I/P) G# N/A (IN REAR LAMPS HARNESS) GRN WIRE HAZARD HAZARD FLASHER HEAD HEADLIGHT SWITCH HOT AT ALL TIMES HOT IN RUN OR START INSTRUMENT CLUSTER LEFT BACKUP LAMP RIGHT BACKUP LAMP LEFT FRONT MARKER LAMP LEFT LICENSE LAMP LEFT PARK LAMP LEFT TAIL/STOP TURN LAMP LEFT TURN INDICATOR LT BLU WIRE LT LT NORMAL OFF ORG/ WIRE PARK PPL PROVISIONS FOR CLEARANCE LAMPS PROVISIONS FOR REAR MARKER LAMPS RIGHT FRONT MARKER LAMP RIGHT FRONT PARK/ TURN LAMP LEFT FRONT PARK/ TURN LAMP RIGHT LICENSE LAMP RIGHT PARK LAMP RIGHT TAIL/STOP TURN LAMP RIGHT TURN INDICATOR STOP/ HAZ FUSE STOPLAMP SWITCH (ON BRAKE PEDAL SUPPORT BRACKET) TAIL LPS FUSE TURN LEFT TURN RIGHT TURN SIGNAL FLASHER TURN-B/U FUSE TURN/HAZARD SWITCH (ON MULTI- FUNCTION LEVER) WHT WIRE YEL WIRE

BACKUP LAMP SWITCH (ON STEERING COLUMN) BLK WIRE BLU WIRE BRN WIRE DK BLU WIRE DK GRN WIRE FUSE BLOCK- I/P G# N/A (REAR LAMPS HARNESS) GRN WIRE HAZARD HAZARD FLASHER (TOP LEFT SIDE OF SHIPPING PANEL) HEAD OFF HEADLIGHT SWITCH HOT AT ALL TIMES HOT IN RUN OR START INSTRUMENT CLUSTER LEFT FRONT MARKER LAMP LEFT LICENSE LAMP RIGHT LICENSE LAMP LEFT TAIL/STOP TURN LAMP LEFT TURN INDICATOR LT BLU WIRE LT LT NORMAL ORG/ WIRE PARK PPL PROVISIONS FOR BODY BUILDER ADDED LAMPS PROVISIONS FOR REAR MARKER LAMPS RIGHT BACKUP LAMP LEFT BACKUP LAMP RIGHT FRONT MARKER LAMP RIGHT FRONT PARK/ TURN LAMP LEFT FRONT PARK/ TURN LAMP RIGHT TAIL/STOP TURN LAMP RIGHT TURN INDICATOR STOP/ HAZ FUSE STOPLAMP SWITCH (ON BRAKE PEDAL SUPPORT) TAIL LPS FUSE TURN LEFT TURN RIGHT TURN SIGNAL FLASHER TURN-B/U FUSE TURN/HAZARD SWITCH (UPPER LEFT SIDE OF STEERING COLUMN) WHT WIRE YEL WIRE

BLK WIRE DAYTIME RUNNING LAMPS CONTROL MODULE (ATTACHED TO I/P HARNESS) DAYTIME RUNNING LAMPS RELAY (LEFT SIDE OF DASH, ON RELAY BRACKET) DIODE NETWORK (ON I/P HARNESS) DK BLU WIRE DK GRN/WHT WIRE DRL INDICATOR FUSE BLOCK BREAKOUT) FUSIBLE LINK (16 GA- GAUGES FUSE 8 GRN WIRE HEADLAMP DIMMER SWITCH HEADLAMPS SWITCH OFF HI BEAM INDICATOR HI LO HOT AT ALL TIMES HOT IN RUN OR START I/P FUSE BLOCK IGNITION SWITCH INSTRUMENT CLUSTER LEFT HEAD- LAMP LO HI LOCK OFF LT BLU WIRE LT GRN WIRE LT GRN/BLK WIRE LT LT ORG/ WIRE PARK BRAKE IN FOG LAMPS PARK BRAKE INDICATOR SWITCH (ON PARK BRAKE LEVER) PARK HEAD PNK IGNITION LAMP FEED HI BM INPUT HI BM INDICATOR RELAY CONTROL GROUND WIRE PNK WIRE RED WIRE RIGHT HEAD- LAMP RUN WIRE TAN WIRE WHT WIRE YEL WIRE

BLK WIRE FUSIBLE LINK (16 GA- GRN WIRE HEAD HEADLAMPS SWITCH HI BEAM INDICATOR HOT AT ALL TIMES INSTRUMENT CLUSTER LEFT HEADLAMP HI LO HEADLAMPS DIMMER SWITCH LT GRN WIRE OFF PARK RED WIRE RIGHT HEADLAMP HI LO TAN WIRE YEL WIRE

3 121 PNK WIRE ACCY BLK WIRE BLK/RED WIRE BLK/YEL WIRE BRN WIRE BRN/WHT WIRE BULB TEST DISTRIBUTOR (CENTER REAR OF ENGINE) DK BLU WIRE DK GRN/WHT WIRE ENGINE COOLANT TEMPERATURE SENSOR (TOP FRONT OF ENGINE) FUSE BLOCK GAGES FUSE GRY WIRE HOT AT ALL TIMES HOT IN RUN, BULB TEST OR START IGNITION COIL (TOP RIGHT REAR OF ENGINE) IGNITION SWITCH INSTRUMENT CLUSTER KNOCK SENSOR (LEFT REAR OF ENGINE, NEAR OIL PRESSURE SENDER) LOCK OFF LT BLU/WHT WIRE LT GRN WIRE MALFUNCTION (SERVICE ENGINE SOON) INDICATOR MANIFOLD ABSOLUTE PRESSURE SENSOR (ABOVE VALVE COVER) NCA WIRE ORG/ WIRE PNK 22 23 WIRE PNK WIRE PNK/BLK WIRE PPL PPL 20 21 PPL 3 4 PPL/WHT WIRE PROVISIONS FOR TACHOMETER RED WIRE RED/BLK WIRE RUN WIRE TAN/BLK WIRE TCC/BRAKE SWITCH (ON BRAKE PEDAL SUPPORT BRACKET) THROTTLE POSITION SENSOR (ON THROTTLE BODY) TRANS FUSE WHT WIRE WHT/BLK WIRE YEL WIRE YEL/BLK WIRE

4.3L 5.7L 5.7L ONLY 4.3L ONLY 7.4L 7.4L ONLY AIR CONDITION- ING SYSTEM BLK WIRE BLK/RED WIRE BLK/WHT WIRE BLK/YEL WIRE BRN WIRE BRN/WHT WIRE CRUISE CONTROL SYSTEM CRUISE SIGNAL DIAGNOSTIC TEST TP SENSOR SIGNAL INJECTOR 1 CONTROL DK BLU WIRE DK BLU/WHT WIRE DK GRN WIRE DK GRN/WHT WIRE DK GRN/YEL WIRE ECM CRNK FUSE ECM BAT FUSE EGR CONTROL EGR ELECTONIC VACUUM REGULATOR SOLENIOD VALVE (TOP RIGHT FRONT OF ENGINE) EVAPORATIVE CANISTER PURGE CONTROL SOLENOID (TOP RIGHT SIDE OF ENGINE) EXHAUST GAS RECIRCULATION VALVE SOLENOID (TOP RIGHT SIDE OF ENGINE) FUEL PUMP RELAY CTRL PCS LOW FUEL PUMP SIGNAL MAP SIGNAL FUSE BLOCK GRY WIRE GRY/RED WIRE HOT AT ALL TIMES HOT IN RUN, BULB TEST OR START IC BYPASS SENSOR GROUND SENSOR GROUND TFT SIGNAL IDLE AIR CONTROL ACTUATOR (TOP REAR OF ENGINE) INJ FUSE KNOCK SENSOR INPUT ECT SIGNAL KNOCK SIGNAL EGR PINTLE POSITION SIGNAL LINEAR EGR VACUUM REGULATOR SOLENOID VALVE (TOP FRONT OF ENGINE) LT BLU/BLK WIRE LT BLU/WHT WIRE LT GRN WIRE LT GRN/BLK WIRE LT GRN/WHT WIRE ORG/ WIRE OXYGEN SENSOR GROUND PNK 26 27 WIRE PNK WIRE PNK/BLK WIRE POWERTRAIN CONTROL MODULE (LEFT SIDE OF SHIPPING PANEL) PPL PPL 24 25 PPL/WHT WIRE RANGE SIGNAL A INPUT SPEED SIGNAL HIGH INPUT SPEED SIGNAL LOW RANGE SIGNAL B RANGE SIGNAL C MIL CONTROL RED WIRE RED/BLK WIRE TAN WIRE TAN/BLK WIRE THROTTLE BODY FUEL INJECTOR #1 (TOP OF THROTTLE BODY UNIT) THROTTLE BODY FUEL INJECTOR #2 (TOP OF THROTTLE BODY UNIT) TRANSMISSION INPUT SPEED SENSOR (NO LOCATION) WHT WIRE WHT/BLK WIRE YEL WIRE YEL/BLK WIRE

3 121 PNK WIRE 4.3L AND 7.4L 5.7L ACCY ALT FUSE BLK WIRE BLK/RED WIRE BLK/YEL WIRE BRN WIRE BRN/WHT WIRE BULB TEST DISTRIBUTOR (CENTER REAR OF ENGINE) DK BLU WIRE DK GRN WIRE DK GRN/WHT WIRE ENGINE COOLANT TEMPERATURE SENSOR (TOP FRONT OF ENGINE) FUSE BLOCK GRY WIRE HOT AT ALL TIMES HOT IN RUN, BULB TEST OR START IDLE SPEED ACTUATOR CONTROL SOLENOID (NO LOCATION AVAILABLE) IGNITION COIL (TOP RIGHT REAR OF ENGINE) IGNITION SWITCH INSTRUMENT CLUSTER KNOCK SENSOR (LEFT REAR OF ENGINE, NEAR OIL PRESSURE SENDER) KNOCK SENSOR MODULE (TOP RIGHT SIDE OF ENGINE) LOCK OFF LT BLU/WHT WIRE LT GRN WIRE MALFUNCTION (SERVICE ENGINE SOON) INDICATOR MANIFOLD ABSOLUTE PRESSURE SENSOR (ABOVE VALVE COVER) NCA WIRE ORG/ WIRE PNK 26 27 WIRE PNK WIRE PNK/BLK WIRE PPL PPL 2 3 4 PPL 24 25 PPL/WHT WIRE PROVISIONS FOR TACHOMETER RED WIRE RED/BLK WIRE RUN WIRE TAN/BLK WIRE TCC/BRAKE SWITCH (ON BRAKE PEDAL SUPPORT BRACKET) THROTTLE POSITION SENSOR (ON THROTTLE BODY) TRANS FUSE WHT WIRE WHT/BLK WIRE YEL WIRE YEL/BLK WIRE

5.7L 7.4L 7.4L ONLY AIR CONDITION- ING SYSTEM BLK WIRE BLK/RED WIRE BLK/WHT WIRE BLK/YEL WIRE BRN WIRE BRN/WHT WIRE DIAGNOSTIC TEST TP SENSOR SIGNAL INJECTOR 1 CONTROL DK BLU WIRE DK BLU/WHT WIRE DK GRN WIRE DK GRN/WHT WIRE DK GRN/YEL WIRE ECM BAT FUSE ECM I FUSE ECT SIGNAL EGR CONTROL EVAPORATIVE CANISTER PURGE CONTROL SOLENOID (TOP RIGHT SIDE OF ENGINE) EXHAUST GAS RECIRCULATION VALVE SOLENOID (TOP RIGHT SIDE OF ENGINE) FUEL PUMP RELAY CTRL PCS LOW FUEL PUMP SIGNAL MAP SIGNAL FUSE BLOCK GRY WIRE GRY/RED WIRE HOT AT ALL TIMES HOT IN RUN, BULB TEST OR START IC BYPASS SENSOR GROUND SENSOR GROUND TFT SIGNAL 470 455 PPL IDLE AIR CONTROL ACTUATOR (TOP REAR OF ENGINE) IDLE SPEED ACTUATOR CONTROL SOLENOID (NO LOCATION AVAILABLE) KNOCK SIGNAL EGR PINTLE POSITION SIGNAL LINEAR EGR VACUUM REGULATOR SOLENOID VALVE (TOP FRONT OF ENGINE) LT BLU/BLK WIRE LT BLU/WHT WIRE LT GRN WIRE LT GRN/BLK WIRE LT GRN/WHT WIRE NCA WIRE ORG/ WIRE OXYGEN SENSOR (IN EXHAUST MANIFOLD) OXYGEN SENSOR GROUND PNK 22 23 WIRE PNK RANGE SIGNAL A INPUT SPEED SIGNAL HIGH INPUT SPEED SIGNAL LOW WIRE PNK/BLK WIRE POWERTRAIN CONTROL MODULE (LEFT SIDE OF SHIPPING PANEL) PPL PPL 20 21 PPL/WHT WIRE RANGE SIGNAL B RANGE SIGNAL C MIL CONTROL RED WIRE RED/BLK WIRE TAN WIRE TAN/BLK WIRE TAN/WHT WIRE THROTTLE BODY FUEL INJECTOR #1 (TOP OF THROTTLE BODY UNIT) THROTTLE BODY FUEL INJECTOR #2 (TOP OF THROTTLE BODY UNIT) TRANSMISSION INPUT SPEED SENSOR (LEFT SIDE OF TRANSMISSION) WHT WIRE WHT/BLK WIRE YEL WIRE YEL/BLK WIRE

3 121 PNK WIRE ACCY BLK WIRE BLK/RED WIRE BLK/YEL WIRE BRN WIRE BRN/WHT WIRE BULB TEST DISTRIBUTOR (CENTER REAR OF ENGINE) DK BLU WIRE DK GRN/WHT WIRE ENGINE COOLANT TEMPERATURE SENSOR (TOP FRONT OF ENGINE) FUSE BLOCK GAGES FUSE GRY WIRE HOT AT ALL TIMES HOT IN RUN, BULB TEST OR START IGNITION COIL (TOP RIGHT REAR OF ENGINE) IGNITION SWITCH INSTRUMENT CLUSTER KNOCK SENSOR (LEFT REAR OF ENGINE, NEAR OIL PRESSURE SENDER) LOCK OFF LT BLU/WHT WIRE LT GRN WIRE MALFUNCTION (SERVICE ENGINE SOON) INDICATOR MANIFOLD ABSOLUTE PRESSURE SENSOR (ABOVE VALVE COVER) NCA WIRE ORG/ WIRE PNK 22 23 WIRE PNK WIRE PNK/BLK WIRE PPL PPL 20 21 PPL 3 4 PPL/WHT WIRE PROVISIONS FOR TACHOMETER RED WIRE RED/BLK WIRE RUN WIRE TAN/BLK WIRE TCC/BRAKE SWITCH (ON BRAKE PEDAL SUPPORT BRACKET) THROTTLE POSITION SENSOR (ON THROTTLE BODY) TRANS FUSE WHT WIRE WHT/BLK WIRE YEL WIRE YEL/BLK WIRE