Does it have a air compressor on it? Are the horns on top air actuated also, or electric? Is it air brakes, air over hydraulic brakes, or hydraulic brakes? Usually a GM truck with Factory air compressor will have an air guage where your headlight switch is & the headlight switch is higher on the dash. Also the air wiper switch would be in the area just below the air guage.

Spanky Hardy
Collector Of Fine Old G.M. COE Trucks & Antique Holmes Wreckers

1948 Chevrolet 5700 COE Holmes HD W35 Wrecker
In the Stovebolt Gallery
More pictures on Photobucket

1950 GMC 250 1-Ton
In the Stovebolt Gallery