Chevrolet Low Cab Forward 4500 2019 Series Owner's Manual page 235

234 Vehicle Care
Relays Usage
1 Stop lamp
Relays Usage
2 Daytime
running lamp
Relays Usage
3 Key on
4 TCM
5 Parking / Neutral
6 Wiper main
7 Horn
8 Wiper high low
9 Trailer brake
10 / Rear power
window
11 / Charge (eng run)
12 Power window
13 Head lamp low
14 Vacuum pump
15 Head lamp high
16 Tail lamp
17 Cigar lighter
18 Cornering lamp
19 Power ACC
20 Blower motor