RevBecca,
I have not seen a factory produced dual pie harness so I'm not sure exactly how it's wired, but I would expect a "Y" type of power lead with a single battery connector fitted to one end, and two power supply cables on the other
(one for each of the motors).
If the lead is not pre-assembled it will be necessary to connect both motor power leads together in parallel and then connect them to the single battery lead.
Here's a diagram that Leslie drew up showing most of the connections on a dual pie circuit:
If you could post some pictures of the harness and connectors, we might be able to work out where the lights are supposed to connect.
This lighting diagram might help:
Sometimes, the switch on the throttle is used for reverse, but I don't know if the switch on the dual pie harness is wired for reverse or for the lights.
Alan