Whenever I add anything to a vehicle that I want to be on only when the key is, I wire it straight to the battery for the main powersource then add a relay and have the power switch comming from the ignition switch. This way you have almost 0 amp pull on your ignition component wiring. All the draw is off the battery. As for whether you should put a terminal on it, I always use a large ring terminal on the end of the wire. Nothing special just a crimp on terminal.......if your good at soldering you can solder the terminal to the wire to make it more permenent; however it is not necessary.
This may help you out a little.
