first indicator means connected to said back up safety means operable to indicate connection of {HEAD ~ said back up safety means} to {TAIL ~ a source} of energy 
first indicator means connected to said back up safety means operable to indicate connection of { HEAD ~ said back up safety means } to { TAIL ~ a source } of energy
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH