Issue with Lance battery switch (on panel)

The link you gave is to a solenoid , probably a continuous duty one . They come normally open or normally closed . the two large lugs are power in and power out , the two small ones - one is ground and one is to drive the solenoid either open or closed , its probably attached to the switch on the panel,. check with a meter the two large lugs to see if you have 12 volt , or battery voltage on one or both sides , if only at one and you have tried the switch both ways , check to see if you have voltage at the small positive lug , if not put 12 volts to it that should drive the solenoid shut ,could be a bad switch, if that dosent work check the ground to the solenoid . If all else fails replace the solenoid . in the mean time you can tie the wires from the large lugs toghether and you should have power to the 12 volt fuse panel

Good luck