There is a switch on your steering column with two wires. I know one is purple. The other may be black? I forget. You'll find it.
When the factory moved this switch down to the transmission, these wires were routed through unused ports of the bulkhead connector where all the wiper motor wires are. You should already have the brown wire from your starter relay to the middle post of the later model neutral safety switch. The two reverse wires are taped in with it and go to the other two posts of that switch, either wire on either post.
