A rotary switch could be used to tap into a string of resistors that total
10k ohm. The tap (wiper) of switch would go to the wire usually connected
to the old power pot wiper. The old power pot would be removed,and flat
cable run out to back of radio as stated before. Should be room there for a
small wafer switch. It would be easy to do for say four levels using a four
position toggle sw if you can find one. I always carry a screwdriver so did
not bother to mod the radio. Really should before FD.