A principal limitation of the prior art systems is the fact that, at low vehicle speeds, {HEAD ~ the electrical generating system} provides {TAIL ~ inadequate operating voltages} to associated signaling devices 
provides
A principal limitation of the prior art systems is the fact that , at low vehicle speeds , { HEAD ~ the electrical generating system } provides { TAIL ~ inadequate operating voltages } to associated signaling devices
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH