This Particular truck, you said it is a 2009 model? that should put it as a Fortis or FT truck, correct.

I believe you should find the connector under the floor board around the break pedal. It should have a four function horn there that also serves as a back up alarm. If this truck shipped with out a back up alarm, you will probably have to turn the function on by accessing the programming either through the dash or the VSM. it may be that the option is only turned off.

These trucks are supposed to have a common wire harness, so I suspect the above to be true. It will be difficult to connect an after market back up alarm, you may have to monitor your reverse pressure via a switch, which you may be able to do be using a pressure test port on the control valve body.

Good luck, and let me know how it turns out.