"Top Mount" refers to where the gauges and valve handles are located on the truck. If you look at the picture, between the cab and the rear body, just in front of the yellow hose, you'll see to what apprears to be an angled panel. There is a cross walk, from the left side of the truck to the right side. The operator will stand there, facing the rear, the controls before them. By placing the controls on top, it gives the operator a better view of the incident scene, and out of the way of traffic. Variations include a side/top mount where the controls are top mounted on one side of the truck, and a rear/top mount.
Added by Andy on 31 December 2009.