So will putting a switch between the wire and the car's wire be a problem?
White Wire— Accessory or ignition wire.
3-2.2.1 OPTION 1 Use a voltmeter to locate a circuit that does not have power when the vehicle is off, but does have power when the vehicle is turned on. This line should be 18 AWG wire and run to the white wire on the PC. This line should be fused at 5A even if it comes from a fuse protected line. It will protect the original circuit if you ever have a short in the line.
3-2.2.2 OPTION 2 Run a second wire from the battery, fused at 5A, with 18AWG wire to a toggle switch and then to the white wire of the PC. Throwing the toggle switch will simulate turning the vehicle on or off.