How to wire 4-wire harness for LED lights on 2015 v for trike rack?

You need a powered trailer harness that combines the brake and turn signals while isolating the power draw like the Curt 56156. Yours will be like the one on the right with more connectors and a rear battery connection.

 

If you want to mount your 4-flat connector on the exterior of your Prius instead of dangling its wires out and closing the hatch door on it, I highly recommend the Hopkins 48595 mounting bracket. It fits nicely on the bottom face of most Toyota bumpers and is easy to install. I paid only $4 for it at an auto parts store. Some Curt 4-flat connectors are not compatible with the Hopkins bracket. I bought a 48" Hopkins 4-flat extension to make it work on our Sienna. The attached photo shows the Hopkins bracket on a Sienna but it could be mounted the same way on a Prius v.

 

I'm paranoid too in that I always lock draw bars to receiver hitches, bike racks to receiver hitches and trailers to vehicles. And I always lock our bikes to our racks with multiple devices when we leave them unattended even for moment. I go as far as to lock the wheels on the bikes to the rack and hitch since bike wheels with disc brakes are very expensive to replace and are a popular theft target. On bikes that have quick release seats, I remove the seats and store them inside the vehicle.

FYI, I had to wrap the 4-flat connector on the Hopkins 4 ft. extension with a bit of electrical tape to make it fit rigidly without moving in the Hopkins bracket although doing that may not be necessary for your installation. If you can't tell, I'm quite enthusiastic about this cheap Hopkins bracket. It's the best 4-flat connector mounting method I've used.