I've fitted led bulbs to the interior (really recommend those) and also to the sidelight. At the back I've fitted led bulb to the number plate and the reversing light with good success. However the led bulbs doesn't seem to work with the taillight/brake light (same bulb) and the 3rd high level brake light. Either it's not working or its very dim. Any ideas?

You'll probably need to add a resistor ballast to each supply line to get them to work. Because of the low current draw the lighting module is sensing that the globe is blown. Probably also sending A DTC of open circuit or short. MY15
Tyre Pressure Monitoring System (TPMS)
Surround Camera System
InControl Apps soon to be replaced with CarPlay (WIP)
Meridian Premium Surround Sound
Digital Audio Broadcast
Timed Climate
Cruise ECO Data
Follow Me Home Reverse
Extra Features Menu
Picture In Motion
4x4i screen (WIP)
Digital Broadcast TV
Meridian Rear Media with WIFI
Factory Powered Tailgate
Blind Spot Monitoring (BSM)
Reverse Cross Traffic Alert (RCTA)
Electrochromatic Wing Mirrors (WIP)