Originally Posted by wpoll

Looks like you have a few wiring mods back there (with the additional LEDS in the lower bumper).

Not all X5 E53 cars have the same tail light wiring - there are a number of variations based on the model year. There is no such thing as an LED tail fitting that will work correctly on all X5 E53 cars...

I think your best bet will be to un-pin the connectors, then put the pins in one at a time until you get the result you want. Maybe study the wiring diagram (for your exact model year etc.) first...