Workhorse has two Chassis fuse blocks.. One is inside, if you have a "W" chassis with a foot operated parking break it should be near the brake pedal. This is the Aux Panel however .. Either Brake lights or Turn Signals (not sure which) is on this panel though.
The main Chassis panel is under the hood, Top center, it is a plain flat black box with no markings.. Remove the cover, the map of fuses is on the inside of the cover.. There are two bolts at the bottom of the box under the cover, these are 12 volt 30 amp connections should you ever need to know.