Give the fuse holders a swim in cleaning fluid then pull & push the fuses in & out to clean the contacts.
The power to the carb solenoid will come off the A terminal on the key switch ( there are tiny letters on the back of the switch )
Very rare for that part of the switch to go bad.
You should get 12V at the A ( might be more than 1 of them ) terminal when the ignition is on.
There should be 12V at the B terminal all the time
And 12V to the S terminal when the key is in the start position.