The company I work for does harness work for the after market. We use TXL for everything due to it's fire and heat ratings. GXL is also a good choice.
As others have mentioned Waytek is a good place to buy wire. We normally buy our connectors from
www.powerandsignal.com or
www.mouser.com. Mouser is normally who I go with for smaller quanities. If you have trouble finding a connector you need let me know.