Our 250 AMP dual battery controller includes a three position switch to control the second battery through the operation of the solenoid.

1. Switch position one isolates the auxiliary battery.  No light.
2. Position two connects the auxiliary battery while the ignition is on.  Green light.
3. Position three connects the auxiliary battery at all times.  Red light.

Kit includes solenoid, toggle switch, pre-terminated wire/connectors, fuse holder, fuse and mounting hardware.  

Note: Solenoid draw is 2.5 AMP while engaged.  If left engaged (battery connected) with vehicle not running it will drain the battery.