On Thu, 25 May 2017 09:29:03 +0100, Harry Bloomfield wrote:

Brian Gaff formulated the question :
However the current drain of modern lights is one heck of a lot less
than a bulb and arguably, less likely to fail without the driver being
alerted via a snazzy dasboard icon.

More than just snazzy, the system can be very practical, very useful. I
can plug the caravan in and know all the car and all the caravan's road
lighting is functioning. If there were a failure on route, I would know
immediately and know precisely which lamp had failed.

They don't even have to completely fail, a poor connection or flickering
lamp is enough to trigger a fault condition.

Just wondering - which car has that on? Im aware of the ones that
register a failed indicator bulb but not ones that show that trailer/
caravan road lighting/reversing/fog lights are working.

As an aside I watched a 17 plate Volvo tractor/trailer unit having its
lights checked at a service station the other day. Driver stood at the
back with a remote control and then went through the checks for all the
trailer lights. Fascinating to watch them all going off and on in
sequence including the side marker lights.