GMC Pickup K2500 (1985-2000) trans- mission circuit Wiring diagrams

2-HI IND 2-HI SW 4 LO INDIC CTRL 4 LO SW 4 LOW SELECT SW IN 2 HI SELECT SW IN 4 HI SELECT SW IN BATTERY IN 4-HI IND 4-HI SW 4-LO IND ANTI-LOCK BRAKES SYSTEM AXLE SIG BLK WIRE BLK/WHT WIRE BRN WIRE BRN/WHT WIRE CHANNEL A CHANNEL B CHANNEL C CHANNEL P DATA LINK CONNECTOR (PARTIAL) (UNDER LEFT SIDE OF DASH) DIESEL DK BLU/WHT WIRE DK GRN/WHT WIRE FRONT AXLE ACTUATOR FRONT AXLE SWITCH FUSE 24 GASOLINE GAUGES FUSE 4 GROUND GROUND GROUND BATTERY IN BATTERY IN PNP SW-P/N IN GRY WIRE GRY/BLK WIRE HEADLAMP, PANEL DIMMER SWITCH HOT AT ALL TIMES HOT IN RUN HOT IN RUN OR START I/P FUSE BLOCK (UNDER LEFT SIDE OF DASH) IGNITION IN ENCODER GROUND GROUND 2 HI INDIC CTRL 4 HI INDIC CTRL ILLUMINATION LAMP LOW SIG LT GRN WIRE LT GRN/BLK WIRE ORG/ WIRE PARK/NEUTRAL POSITION SWITCH (ON LEFT SIDE, CENTER OF TRANSMISSION) PNK WIRE POWERTRAIN CONTROL MODULE (DIESEL) PPL/WHT WIRE RED WIRE RED/WHT WIRE SPARE POWER SOURCE AUXILIARY BATTERY RELAY TAN/BLK WIRE TCASE FUSE 2 TCC/STOP LAMP SWITCH (TOP OF BRAKE PEDAL) TRANS- MISSION CIRCUIT TRANSFER CASE CONTROL MODULE (STEERING COLUMN BRACKET) TRANSFER CASE ENCODER (RIGHT SIDE CENTER OF TRANSFER CASE) TRANSFER CASE ENCODER MOTOR (RIGHT SIDE OF TRANSFER CASE) TRANSFER CASE SELECT SWITCH TRANSFER CASE SWITCH (TOP LEFT OF TRANSFER CASE) TURN B/U FUSE 16 TURN SIGNAL SWITCH WHT WIRE YEL WIRE YEL/BLK WIRE

2-HI IND 2-HI SW 4 LO INDIC CTRL 4 LO SW 4 LOW SELECT SW IN 2 HI SELECT SW IN 4 HI SELECT SW IN BATTERY IN 4-HI IND 4-HI SW 4-LO IND ANTI-LOCK BRAKES SYSTEM AXLE SIG BLK WIRE BLK/WHT WIRE BRN WIRE BRN/WHT WIRE CHANNEL A CHANNEL B CHANNEL C CHANNEL P DATA LINK CONNECTOR (PARTIAL) (UNDER LEFT SIDE OF DASH) DIESEL DK BLU/WHT WIRE DK GRN/WHT WIRE FRONT AXLE ACTUATOR FRONT AXLE SWITCH FUSE 24 GASOLINE GAUGES FUSE 4 GROUND GROUND GROUND BATTERY IN BATTERY IN PNP SW-P/N IN GRY WIRE GRY/BLK WIRE HEADLAMP, PANEL DIMMER SWITCH HOT AT ALL TIMES HOT IN RUN HOT IN RUN OR START I/P FUSE BLOCK (UNDER LEFT SIDE OF DASH) IGNITION IN ENCODER GROUND GROUND 2 HI INDIC CTRL 4 HI INDIC CTRL ILLUMINATION LAMP LOW SIG LT GRN WIRE LT GRN/BLK WIRE ORG/ WIRE PARK/NEUTRAL POSITION SWITCH (ON LEFT SIDE, CENTER OF TRANSMISSION) PNK WIRE POWERTRAIN CONTROL MODULE (DIESEL) PPL/WHT WIRE RED WIRE RED/WHT WIRE SPARE POWER SOURCE AUXILIARY BATTERY RELAY TAN/BLK WIRE TCASE FUSE 2 TCC/STOP LAMP SWITCH (TOP OF BRAKE PEDAL) TRANS- MISSION CIRCUIT TRANSFER CASE CONTROL MODULE (STEERING COLUMN BRACKET) TRANSFER CASE ENCODER (RIGHT SIDE CENTER OF TRANSFER CASE) TRANSFER CASE ENCODER MOTOR (RIGHT SIDE OF TRANSFER CASE) TRANSFER CASE SELECT SWITCH TRANSFER CASE SWITCH (TOP LEFT OF TRANSFER CASE) TURN B/U FUSE 16 TURN SIGNAL SWITCH WHT WIRE YEL WIRE YEL/BLK WIRE

2-HI IND 2-HI SW 4 LO INDIC CTRL 4 LO SW 4 LOW SELECT SW IN 2 HI SELECT SW IN 4 HI SELECT SW IN BATTERY IN 4-HI IND 4-HI SW 4-LO IND ANTI-LOCK BRAKES SYSTEM AXLE SIG BLK WIRE BLK/WHT WIRE BRN WIRE BRN/WHT WIRE CHANNEL A CHANNEL B CHANNEL C CHANNEL P DATA LINK CONNECTOR (PARTIAL) (UNDER LEFT SIDE OF DASH) DIESEL DK BLU/WHT WIRE DK GRN/WHT WIRE FRONT AXLE ACTUATOR FRONT AXLE SWITCH FUSE 24 GASOLINE GAUGES FUSE 4 GROUND GROUND GROUND BATTERY IN BATTERY IN PNP SW-P/N IN GRY WIRE GRY/BLK WIRE HEADLAMP, PANEL DIMMER SWITCH HOT AT ALL TIMES HOT IN RUN HOT IN RUN OR START I/P FUSE BLOCK (UNDER LEFT SIDE OF DASH) IGNITION IN ENCODER GROUND GROUND 2 HI INDIC CTRL 4 HI INDIC CTRL ILLUMINATION LAMP LOW SIG LT GRN WIRE LT GRN/BLK WIRE ORG/ WIRE PARK/NEUTRAL POSITION SWITCH (ON LEFT SIDE, CENTER OF TRANSMISSION) PNK WIRE POWERTRAIN CONTROL MODULE (DIESEL) PPL/WHT WIRE RED WIRE RED/WHT WIRE SPARE POWER SOURCE AUXILIARY BATTERY RELAY TAN/BLK WIRE TCASE FUSE 2 TCC/STOP LAMP SWITCH (TOP OF BRAKE PEDAL) TRANS- MISSION CIRCUIT TRANSFER CASE CONTROL MODULE (STEERING COLUMN BRACKET) TRANSFER CASE ENCODER (RIGHT SIDE CENTER OF TRANSFER CASE) TRANSFER CASE ENCODER MOTOR (RIGHT SIDE OF TRANSFER CASE) TRANSFER CASE SELECT SWITCH TRANSFER CASE SWITCH (TOP LEFT OF TRANSFER CASE) TURN B/U FUSE 16 TURN SIGNAL SWITCH WHT WIRE YEL WIRE YEL/BLK WIRE

2-HI IND 2-HI SW 4 LO INDIC CTRL 4 LO SW 4 LOW SELECT SW IN 2 HI SELECT SW IN 4 HI SELECT SW IN BATTERY IN 4-HI IND 4-HI SW 4-LO IND ANTI-LOCK BRAKES SYSTEM AXLE SIG BLK WIRE BLK/WHT WIRE BRN WIRE BRN/WHT WIRE CHANNEL A CHANNEL B CHANNEL C CHANNEL P DATA LINK CONNECTOR (PARTIAL) (UNDER LEFT SIDE OF DASH) DIESEL DK BLU/WHT WIRE DK GRN/WHT WIRE FRONT AXLE ACTUATOR FRONT AXLE SWITCH FUSE 24 GASOLINE GAUGES FUSE 4 GROUND GROUND GROUND BATTERY IN BATTERY IN PNP SW-P/N IN GRY WIRE GRY/BLK WIRE HEADLAMP, PANEL DIMMER SWITCH HOT AT ALL TIMES HOT IN RUN HOT IN RUN OR START I/P FUSE BLOCK (UNDER LEFT SIDE OF DASH) IGNITION IN ENCODER GROUND GROUND 2 HI INDIC CTRL 4 HI INDIC CTRL ILLUMINATION LAMP LOW SIG LT GRN WIRE LT GRN/BLK WIRE ORG/ WIRE PARK/NEUTRAL POSITION SWITCH (ON LEFT SIDE, CENTER OF TRANSMISSION) PNK WIRE POWERTRAIN CONTROL MODULE (DIESEL) PPL/WHT WIRE RED WIRE RED/WHT WIRE SPARE POWER SOURCE AUXILIARY BATTERY RELAY TAN/BLK WIRE TCASE FUSE 2 TCC/STOP LAMP SWITCH (TOP OF BRAKE PEDAL) TRANS- MISSION CIRCUIT TRANSFER CASE CONTROL MODULE (STEERING COLUMN BRACKET) TRANSFER CASE ENCODER (RIGHT SIDE CENTER OF TRANSFER CASE) TRANSFER CASE ENCODER MOTOR (RIGHT SIDE OF TRANSFER CASE) TRANSFER CASE SELECT SWITCH TRANSFER CASE SWITCH (TOP LEFT OF TRANSFER CASE) TURN B/U FUSE 16 TURN SIGNAL SWITCH WHT WIRE YEL WIRE YEL/BLK WIRE

2-HI IND 2-HI SW 4 LO INDIC CTRL 4 LO SW 4 LOW SELECT SW IN 2 HI SELECT SW IN 4 HI SELECT SW IN BATTERY IN 4-HI IND 4-HI SW 4-LO IND 5 CM FROM TRANSFER CASE RELAY BREAKOUT FROM AXLE SWITCH) 79 CM FROM ENGINE HARNESS BREAK-OUT) BLK WIRE BLK/WHT WIRE BRN WIRE BRN/WHT WIRE CHANNEL A CHANNEL B CHANNEL C CHANNEL P DATA LINK CONNECTOR (PARTIAL) (UNDER LEFT SIDE OF DASH) DIESEL DK BLU/WHT WIRE DK GRN/WHT WIRE FRONT AXLE ACTUATOR FRONT AXLE SWITCH FRONT AXLE SWITCH (RIGHT REAR OF FRONT DRIVE AXLE) FUSE 24 GASOLINE GAUGES FUSE 4 GROUND GROUND GROUND BATTERY IN BATTERY IN PNP SWITCH OUT GRY WIRE GRY/BLK WIRE HEADLAMP, PANEL DIMMER SWITCH HOT AT ALL TIMES HOT IN RUN HOT IN RUN OR START I/P FUSE BLOCK (UNDER LEFT SIDE OF DASH) ILLUMINATION LAMP LT BLU WIRE LT GRN WIRE ORG (OR LT GRN/BLK) WIRE ORG/ WIRE PARK/NEUTRAL POSITION SWITCH (ON LEFT SIDE, CENTER OF TRANSMISSION) PNK IGNITION IN ENCODER GROUND GROUND 2 HI INDIC CTRL 4 HI INDIC CTRL WIRE PNK WIRE POWERTRAIN CONTROL MODULE (DIESEL) PPL/WHT WIRE REAR LIFTGATE WINDOW RELEASE CIRCUIT RED WIRE RED/WHT WIRE SPARE POWER SOURCE AUXILIARY BATTERY RELAY SPARE POWER SOURCE TAN/BLK WIRE TCASE FUSE 2 TCC/STOP LAMP SWITCH (TOP OF BRAKE PEDAL) TRANS- MISSION CIRCUIT TRANSFER CASE CONTROL MODULE (STEERING COLUMN BRACKET) TRANSFER CASE ENCODER (LEFT SIDE CENTER OF TRANSFER CASE) TRANSFER CASE ENCODER MOTOR (LEFT SIDE OF TRANSFER CASE) TRANSFER CASE RELAY (1-TON VEHICLES ONLY) (RIGHT SIDE OF FIREWALL) TRANSFER CASE SELECT SWITCH TRANSFER CASE SWITCH (TOP LEFT OF TRANSFER CASE) TRANSFER CASE SYNCHRONIZER (TOP OF TRANSFER CASE) TURN B/U FUSE 16 TURN SIGNAL SWITCH WHT WIRE YEL WIRE YEL/BLK WIRE