That's what it was guys. Unfortunately I bought this bike used so it is missing one. I just put it on the right side since that is the most obvious side when it is parked and locked.

THANKS!!!!

 

2010 FLHX-Sony DSX-S310BTX-Soundstream PN4.520D-Polk MM651.pdf

Under the wiring section, item 7 reads:
"7. Connect the left crossover black/white wire to the green/black wire on the PN4.520D speaker harness. Connect the left crossover black wire to theGreen wire on the PN4.520D speaker harness. Connect the right crossover black/white wire to the violet wire on the PN4.520D speaker harness. Connect the right crossover black wire to the violet/black wire on the PN4.520D speaker harness. Tape up the remaining speaker wires coming off the wiring harness."

There is no output wire speaker harness off the PN4.520D amp. The only wire harness for the amp is for the line-level inputs.
The speakers need to be wired to the black connection block on the amp.

This PDF mentioned above makes reference to it, but the others where the SS PN4.520D amp is part of the install also do as well...

 

yeah those instructions were put together when SS was shipping amps that had speaker harnesses coming out the side of it. Now they're using the terminal blocks. I'll try and update them all over the weekend.