Bopper

Hello Ive just bought a class 86 off ebay ,but it had a module fitted that was for dcc ,so Ive taken this off ,because the seller forgot to do so,now the wiring is ,a red wire coming from the left hand side of the motor going to the front connection on the roof switch,a brown wire coming from the rear bogie to the back connection on the switch,and a black wire from the right hand side of the motor thats just not connected?