Wiring to light switch melting

[HiCube4]

I am sure this has been raised before as a lot of guys i've asked about it seem to think its a common fault with Transits, BUT, wht the hell does this happen????? My HiCube earns a living driving all over the UK, sometimes in the dark, especially this time of year, and while speeding along the A11 today I caught a waft of plastic burning, thinking it was outside, closed the window and it got worse, emptied the cab of clutter as I thought I had the heater blowing on some delicate item no change, only when i put my nose to its primary function did I find the wiring to the light switch was in serious meltdown, 2 of the smallest wires carrying all the current for ALL the lights seemed to have called it a day and fried themselves up, ANYONE have a clue??????/

[MrMPuk]

Due to a poor connection within the switch which causes higher resistance and heat.

[mikke]

When i eventually finish fitting my new led rear lights into the back
of the van. ive wired off the wiring for the wally light.
im guessing it was fitted by ford as the wires and the switch are factory looking.
im hoping the fuse that runs them will be man anoth.
as it was after all powering a motorized wally light.
can any shed in light on this
excuse the pun

[MrMPuk]

What's a wally light and what does it have to do with HiCube4's question?

[HiCube4]

Thanks for the replys, have fitted new switch as this happened just after purchase, 2006, and putting a new connection on the old wiring that had fried the plug, only for it to reappear, 1997 2.5Di 156,000miles

[MrMPuk]

new or second hand?