Ok sorry but you have me a bit confused, at first you mentioned you needed a RAP relay, then when you said the tech did troubleshooting ha said "He did the trouble shooting and told me the RAP was the issue."
Now you are saying you need the RAP to make it work.
What you mentioned that was in the car is just steering wheel interface controls.
If it were me I'd just get something to handle RAP, and the steering wheel interface controls altogether, the one I suggested will do both, but the thing is to help verify it will work I need more info, which I have asked for, and you have not provided.
I asked what Model of head unit you bought, I need to know the brand and model number to be sure the RAP/Steering Wheel controls will function correctly.
I can only help you if you help me, I may not work at Best Buy installing car audio, but in my younger teen years I installed systems in all of my friends cars, I even dropped a 9,000.00 Competition system in my Park Ave, so I do know a bit.
And from what I know I have never heard of radio power coming from a steering wheel interface device, yes that device gets power fed to it, but it should be from a switched 12v power source, which would be one of the switched fuses in the fuse box.
The head units power should be coming from the wiring harness you bought to connect your factory wiring to the aftermarket head unit.
Or it would be going through a RAP relay, which lets the power to the radio stay on after you turn the key off, until you open a door..
Sometimes it also controls power windows, and interior lighting in the same manner.
If your radio is not one of these models, then it should not work right with the steering wheel control interface that you have.
"Steering Wheel Control Interface for Alpine, JVC, Clarion, Kenwood, Pioneer, Sony, Valor, OEM, Boyo, Dual, Visteon, Advent & Blaupunkt Radios"
It is known not to work with these Sony models if you have a Sony.
XAV-7W, CDX-MP80, CDX-MP70, CDX-M850MP, CDX-M3DI, CDX-M800, CDX-CA900X, MEX-5D1, MEX-1HD,CDX-M730, CDX-M770, CDX-M7815X, CDX-M620, CDX-M670, CDX-CA850X, CDX-M9905X, CDX-CA860X."
If it is another model other than what is listed then to retain steering wheel controls you need you'd need this one.
With that said ask your audio guy if the one I linked on the first page for you will work.
Ignore the first ones that we posted, they are not what you are looking for.