It's not feasible to rebuild a rusty switch for a customer and stand behind your 'rebuild" if you are not experienced. Buy the original 12V or 6V version of the original switch, put his original knob and shaft in it and install it.
Don't worry about a fuse. Some switches have a resetting thermal overload bimetal strip and/or you or your harness can fuse the necessary circuits. The original 54 had two fuses on a fuse holder, one for tail lights, one for brake lights.
What harness are you going to use? Did you get my private message?
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn
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