2014 Limited. Is there a connector in the fairing that I can tap into to get access to the rear speakers or should I buy the complete harness from Biketronics to hook up the BT355?

 

Nope no rear speaker access in the fairing unless you get the BT harness or cut into the wiring.
The other alternative is to run extra speaker wire from the rear back to the front and then back but that is a PITA

 

If you're up for mounting a small amp in the tour pak, you can use the existing wires in the pods to feed the amp. Then just run new wires into the pods to feed the speakers.
You will need to run pos and neg wires though to feed the amp. Just use disconnects so you can remove the tour pak.