Mirror Arm Looms Without Plugs
Optimill Heated Mirror Arm Wiring Looms for Land Rover Defender.
These are specifically designed to wire up the puddle lights and heated mirrors into the Land Rover factory wiring. The loom means the puddle lights come on and off with opening/closing the door and when the vehicle is locked/unlocked.
This version will require soldering the wires together where the loom meets the wire coming through the door from the mirror arm.
Also available: MUD Heated Mirror Pads that fit into your existing mirrors. Peel off the backing and stick the element to the back of your Defender mirror glass.