Defender 90 lights not working

I have a 2001 Defender 90 TD5. In the winter the headlights stopped working on a snowy night but were OK the next day and until a week ago. (6 Months). After much troubleshooting, I find the brown/blue 12v supply to the switch is not live. I have checked fuses. My garage told me it was the blue block on the picture which is slightly brown and melted. This appears to be a commoning block and has 2 rows of 10 wires. The power to the switch is brown/blue, and there is a similar wire visible to this block (2nd from the end). There is no slack in the wires and I cant get it out enough to access it. It won't move in any direction apart from twisting it around. I have tried to take the bottom of the dash out but the bit directly above the fuse box won't budge.

Can anyone confirm this block is where power comes from to the light switch? Has anyone had a similar problem? Has anyone any suggestions on how I can get access? I am thinking of running a new supply to the switch might be the most straightforward answer, I have tested this theory by connecting a temporary wire from the switch to the battery. Any help much appreciated.

The plot thickens. Apart from unsuccessfully trying to get at this blue block I have not changed anything. Last night when I tried to lock it, the central locking did not lock, instead the the extra head lights fitted on the A frame flashed. Am going to trace the wires back from them to see where they go.

And with Defenders it is always worth earth connections to chassis/body

I managed to get the blue header apart by breaking it. It has 4 multi finger plates in it that short 4 sets if wires together. One of them has melted plastic on it, when I pulled it out and put it in the other way round the lights started working apart from those on the A frame so I have clearly introduced a fault to them. Although the lights were working the section of header previously melted gets very hot so clearly there is high resistance on those pins. This would be easy to fix except I can’t get to the wires above the blue header. This must be possible?