Self Fixing Reversing Lights

My reversing lights have not been working for weeks.  After having done the normal stuff the garage assumed that the fault is something to do with the reconditioned gear box and it is booked in on Monday to have an investigation under the gear box warranty.

I know the reversing lights were not working on Friday evening because I remember thinking its getting dark and it would be easier with reversing lights.

Today, Saturday, they have started working.  I first noticed them when my wife was manoeuvring to hook up the harrow in the field, first thing this morning.  Since then the reversing lights have worked every time!

They must know they are booked in to the garage on Monday!  :-)

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Update Sunday:

The reversing lights are still working.

The only thing I did to the Discovery between Friday night and Saturday morning before I notice the lights were working, was to connect my new Nanocom.  I did not make any changes, I just had a nose round to see what the Nanocom could read and make sure it was working.

I have checked the circuit diagram and the reversing lights do not rely on the Body Control Unit (BCU) or any other Electronic Control Unit (ECU) in the car.  There is a feed to the BCU but the switch in the gearbox is what should turn on and off the lights.

I'm still puzzled!

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Update Tuesday:

The reversing lights stopped working again yesterday after I had told the garage there was nothing to fix.  The mysterious self correction was only temporary for the weekend.

Before taking it back to the garage this morning I wanted to check the cables for myself.  I made up and plugged in a simple test loop to short where the switch would normally be.  The lights worked therefore it must be a switch fault...

When I plugged back in the switch it now worked!

As I had not touched the switch just the connector it now pointed to a problem with the joint where the switch cable joined the main loom.   That was difficult to check on my own and Shelley was already at work, so I took it in to the garage as planned. With one person wiggling and another watching the lights the garage confirmed the fault and narrowed it down to the exact point.

With hindsight this should probably have been one of the first things to try but what with having already had a worn out switch a faulty new switch and now faulty cabling it was just too many things going wrong at the same time.

Fingers crossed it is fixed now.