No input available from the multifunction switch will cause the headlights to come on as a fail-safe feature.
Loss of CAN bus communication will do the same thing.
The best way to troubleshoot the headlight system is with the dealer scan tool because the system involves CAN and LIN communications to the TIPM.
Their scan tool can monitor communications and point out where the problem is. Otherwise, you can use a DMM to check for continuity at different points along the various circuits.
2008 Unlimited Rubicon Automatic