GMC 2010 T-Series Owner's Manual page 232

Relay Block C
Relay Block C
1 Parking Brake
Daytime Running Lamps (DRL) On
2
(Engine Run)
Daytime Running Lamps (DRL) Off
3
(Parking)
Parking Lamps/Daytime Running
4
Lamps (DRL)
5 Fuel Filter (Heated Fuel)
6 Stop Lamp
5-84
Usage
Relay Block D
Relay Block D
1 Neutral (Medium Duty Transmission)
Back-up Lamp (Reverse) (Medium
2
Duty Transmission)
Usage