Hi Jani,
mine (1975 model factry RHD) had all the electrical loads passing through the ignition switch - something like 60 amps probably with A/C, wipers, all lights on etc. I first found it when I felt the heat radiating on my knee one cold wet night. The plastic was starting to melt and the terminals nearly fell out of the switch housing. No wiring diagram unfortunately but i put in a big relay and just took all the loads out of the ignition switch. Never been a problem since then (15 years ago). I did have to pull the dash to run some decent size cables from RHS of car (steering side) to fuse box (LHS) where I mounted the relay. Otherwise it was reasonably straightforward.
regards
Peter