On our T5 Camper van conversion I had to replace the side door step which was quite badly worn during it’s previous life as Kombi van. The original step had a courtesy light in the rear end of the step, the after market replacement does not, and its not a simple task to fit one as they are designed to fit into a slight recess, so it’s not just a case of cutting a hole. I considered making a custom foot light unit with white LEDs that would fit there. On consideration I decided not to though. There is already an LED light fitting above the rear sliding door so it would be nice if that were to come on when the door was opened.
The rear lighting in the camper consists of 5 LED units supplied by the leisure battery and switched through its own circuit. One of the LED fittings is directly above the door opening. I need just this one LED fitting to illuminate as a courtesy light. The courtesy light circuit is supplied from the main vehicle battery and that power source should not be mixed with the power from the leisure battery. The answer to this problem is to connect the over door LED to both circuits via a diode from each circuit. Diodes are the electrical equivalent of a 1 way valve, so using a diode between each circuit and the LED will allow it to be powered by either circuit without the power flowing back to the other circuit, keeping the leisure battery light circuit separate from the courtesy light circuit and sharing the one fitting.
A potential problem with the silicon diodes is that there is a forward voltage drop across them of 0.6 volts or more. This would make the over door LED slightly less bright than the others. The solution is to use a Shottkey Diode which has only 0.2V forward voltage drop.
I few months ago I would have been able to pop down to Maplin and buy a couple of diodes, but now I’m having to wait for them to arrive via Internet Mail order and pay almost £5 post and packing (they weigh about 5 grams or less).