I searched Ebay for a "12V Timer Switch" and there were loads of cheap ones from China (no surprise).
I ordered this and it came in just under a week:
It was less that Â£7 delivered, so if it was rubbish I hadn't lost much. Its got manual override for on/off and auto functions. The timer is 7 days and there are about 15 on/off functions, so plenty to play with
I wanted to put it somewhere out of sight, so decided to put it in the cubby under the armrest.
First thing was to take the cubby out, 2 torx screws and a bit of a tug at the front and it was out.
I decided to make a cardboard template first, so that the fit was right.
I then transferred this and cut out some 1.2mm aluminium sheet I had lying around but could have used thin plywood or MDF. I cut a 60mm hole with a hole saw for the front of the timer to go through.
Then I set about wiring the timer up. I took live and negative feeds from the power socket above the ashtray in the centre console (purple/yellow is a permanent live and black is earth).
The FBH is triggered by earthing pin 3, so I ran a wire from there back inside the cabin and behind the centre console and under the armrest.
The switch is just a live and earth and and earth on the output and the trigger wire for the FBH, as its a simple circuit, even I could work it out
I covered the plate with some spare covering I had left over from when I recovered an old parcel shelf and popped it all in place.
I took the opportunity to add an Aux Power Socket I picked up for Â£2.50 on Ebay.
Tested and all working fine. I dont think its too bad for less than Â£7.00. :D