how to reach wires for trailer lights

I have a 2010 Prius. I mounted the hitch for a trailer. I bought a 3 wire to 2 wire adapter. Now I need to connect the adapter to the car. I bought a universal adapter and I need to use splices to connect it. Is there a place where I can reach the wires in the car with enough slack to attach the splices? Or, is there a place where I can buy only the T-connectors (without the adapter) that come with adapters specific to Gen 3 Priuses?