I don't think anybody ever had this exact problem, so I'm not surprised your search was fruitless. So let's troubleshoot it.
The "service 4WD" light comes on if the TCCM doesn't see the sensor feedback voltages it expects from the encoder motor or the front axle actuator. OR if the PCM loses communication with the TCCM.
What happens when you turn your AUX lights on, assuming they are incandescent lamps, is a huge inrush of current that can induce current in any wires running parallel to the power OR ground wires, and also develop a voltage on the ground lug of wherever the aux lights are connected to.
My guess is that surge current is upsetting the TCCM and causing it to quit talking to the PCM.
Can you describe fully how your aux lights are wired? Are you using a relay? Where is the switch? Where does the power come from? What path does the wiring take from the battery to the lights? All the wiring, even the ground. Are you sharing the power or ground connections with any other connections or ring lugs?
I suspect your fix will be just changing the path of the wiring, the tightness of the connections, or something of that nature. I'm working on a test system where I need to accurately measure a 500 Amp pulse, 100 billionths of a second wide (100 nS), without touching the current path because it may have 600 volts on it. So I'm depending on the crosstalk (induced current) from that 500 Amp path to a small inductive loop of wire (embedded in a PCB, actually) placed 0.003" away. We're getting about a 3 volt signal induced in the small loop, and that's very easy to measure with a high speed digitizer.