I have done zero research on this. With that out of the way I'm intrigued by the BCU control. Wouldn't the momentary switch in the binnacle pass a signal to the BCU and tell it to switch ground to the external relay, until it's either pressed again or the power is cycled which would reset the BCU state? I'm guessing this isn't covered in the Electrical Library or the ETM but in theory, as long as you could identify the pinout on the BCU that triggers the aux light relay I would think you could restore the OE control. The number of contacts on the factory relay box is a little troubling but in reality it shouldn't be that complicated. Best, any chance you'd be willing to break one open and post a few pics?

 

The Aux Light LR Wiring harness as far as I know does not interfere with the BCU as it is added at the dealership or it came on the LR say a Kalahari Edition. The only wiring going inside the cabin = for the switch mounted on the binnacle. The Front Fog Lights and the Rear Fog Lights are the ones that go thru the BCU. When enabling the Hi/Lo Beam setting with the Fog Lights you are only messing with the Fog Lights. The Relay the OEM LR Safari 5000 lights use does have a momentary switch, and the relay has 10 pins vs a standard relay which normally has 4-5 pins. That's why I highly recommend using a Cruise Control switch, and the front part to make yourself a latching switch. You do not have to use an OEM switch mounted at the binnacle, but I like a nice clean install. You have the spot down by the HVAC to mount a switch, or anywhere you want it personally. Heck you can even wire up an aux wiring harness to use the Hi/Lo beam wire as the trigger for the relay and bypass a switch all together, but if you enable your high beams for example you can not turn off the aux lights.

When wiring Aux lights it is best to keep it separate from the rest of the electrical system. It keeps things simple, and it doesn't interfere with any of the stock wiring. Get your power directly from the battery, or the fuse block near the battery, ground it, and then run your wires inside to the switch, and to the lights.

 

Ah ok, that could explain all the pins on that relay module. All the control happens in there via the momentary switch. Agreed about the separate wiring harness, always risky to load up on the factory harness for stuff like high wattage lights.