The switch opens {TAIL ~ a solenoid valve} which vents the hydraulic pumps which move the tracks of the trencher in {HEAD ~ the forward direction} 
The switch opens { TAIL ~ a solenoid valve } which vents the hydraulic pumps which move the tracks of the trencher in { HEAD ~ the forward direction }
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD