Battery drain

[DieselHonda]

If I don't drive my car for a week, the car will not start. I seem to have narrowed it down to fuse no6 ( radio and interior lights) in the footwell. I have the switches turned off, removed all the blubs, booth and doors, not the sun visors or glove box, this stop the drain, in September I had the car locked for seven days, with fuse  no6 removed and car started ok.  I have noticed that when the engine is running, tested a few times going to work on a 30 mile journey, with multimeter connected into the lighter socket, I get no more than 13.4 Volts on the DC system. I changed the battery as well at the start of the summer. Any ideas? 

[Trevor]

The voltage is sufficient for internal electrics and I would check all earth leads as well as power leads from the battery to ensure there is no corrosion or damage at the connections.
As per your other post about the alarm system this could be water ingress affecting your internal lights (dripping down through from windscreen or even heater matrix). Check there are no signs of water tracing underneath the dashboard area.