Build your own piACC
Nice Pi Zero Starter Kit with cables: https://amzn.to/2XbhKvg
Relay I used: https://www.robogaia.com/4-relays-ras...
Less expensive 4 channel relay: https://amzn.to/2X2zFUH
Trailer 5 Wire: https://amzn.to/2By1j2Q
Membrane keypad: https://amzn.to/2E9pypH
Crimps: https://amzn.to/2EaSrSs

piACC Vehicle Accessory Controller

piACC is a multi-part system and software suite that allows you to control vehicle accessories without the need to run wiring into the cab of your vehicle.
It can be used on any 12v system with recharging batteries.