Check all the connections to the motor, make sure they are all clean especially the ground. If that doesn't do it, either try the motor on another car or find a replacement that you know works.
I don't have a '69 wiring schematic, but if you can identify the lead wire just put 12 volts to it and stand back. You're just basically taking the switch out of the circuit.
Like jake said, you can make a jumper to run from a switched source to the 12 volt power wire on the side of the motor. I believe it was the bottom blade on my plug, but not sure without looking at a schematic. I thought my problem was the switch, but it turned out to be a bad motor.
You can also remove the plug on the back of the switch and make a jumper from the black wire to either of the others and the motor should come on with the key turned to the on position.
I would have a look at the original wiring by removing the tape on the harness right back to the switch. You may find one bad connection or a bent pin on a connector that can easily be repaired as opposed to trying to rewire the complete assembly and maintain some sort of decent looking wiring harness. Just my $.02
