Never one to leave something alone, I decided just using the red LEDs on that was a waste. So decided to try and use the white LEDs for the courtesy circuit.
Probably lots of ways that I could have done that, but I decided to replicate the existing circuitry with a bridge rectifier, which would mean isolating the existing circuit and adding some pins to connect up the new supply
I went about this by breaking the circuit tracks with a knife, which was made a bit trickier as the negative end of the diodes we're all connected together in a kind of ground plane on the LED side of the board.
Here's how it ended up:
I cleared around the holes where the connection pins are to make sure when I added the two new pins they didn't get connected to anything already on the board.
Then it was just a case of adding another bridge rectifier by gluing it to the board and connecting it up. Added two pins stolen from a right angle header pin either side of the existing ones. I also added another resistor to the red LED circuit as it was a bit bright for ambient lighting. The wiring is a bit of a dog's dinner as I was making it up as I went along, the second one was neater!
Finally wired up a lead, added some crimp connectors and inserting them into the existing plug from the kit. Picked up the courtesy light feeds from the step lights and bingo - white courtesy lights red ambient lights, all with one light fitting.
I've bought another kit now and am going to repeat this but fit them in the rear base of the front seats.