Hi I'm replaced my steering column assembly and I'm just sorting the wiring out
Currently I have
Pin 30 50 X all thick red cables
x is switched live that goes to my fuses and powers every everything and 15 black live to ignition circuit.

New assembly from a 1970 bug has
Thick red cable ( from battery or live feed to lights?)
Black red (to starter motor)
Thin gray ( to buzzer going to ignore)
Thin black ( to ignition circuit)

Question is how do I wire up the new ignition switch so I can have a switched live feed or is that not possible on a pre 1972 ignition switch?

It depends on how many seperate contacts you have on the switch, sold the 71 beetle a few months ago and that only had off, ignition and start positions from memory.

But of googling and think this has answered my question
https://answers.yahoo.com/question/index?qid=20090221173322AAoBsiA

So I'm planning on useing a high amp relay connected to the black switched wire with a new fused supply from the battery. Does this sound sensible or is there a better way?

Later ignition switches had a 30, 15, X and 50.
Basically
30 {Red) is permanent live in to the switch
from battery
15 (Black) is ignition live from switch to fuseboard feeds and coil +very that stays on when you turn ti the starter position.
X (Black / Yellow) is a secondary ignition live to fuseboard feeds but turns off when turn key to starter motor position.
50 (Red / Black) goes to starter motor solenoid.

This is basically so that things like headlights and radio can be fed off X Secondary live so when you try to start the car these feeds are turned off so as much power as possible goes to starter solenoid.

So
Position 1 (ignition on).  30 in. 15 on, X on, 50 off
Position 2 (starter motor)  30 in. 15 on, X off, 50 on

Hope that makes sense.

The older ignition switches didn't have an X so simply everything is fed off 15 (Black)  30(Red) is still in. 50 (Black/red) is still out.

Chad