Apologies for not getting back sooner. I found the existing loom wiring, unfortunately I could not get the dimmer to function correctly and ended up simply wiring the earth side of the lights directly to some new door switches that I installed in the A post (NB: door post is already rebated for the switches). Lights work when the doors are open and extinguished when closed.
I also fitted an override switch next to the cigarette lighter socket to allow the lights to work with the doors shut.
