Reading a 0 - 1V Signal - Weird cable
Just chop the spades off and solder the wires to a 0.1" pin socket and plug it into ADC1 or ADC2 on the Gertboard. If you don't want to destroy the cable that came with the equipment then go down to Radio-shack or Tandy (do they still exist) or Maplin (in the UK and maybe elsewhere) and buy a cheap RCA cable and butcher this to suit your needs.

Or buy an RCA to RCA cable and get one of these: -



Source of RCA break out boards