@LeeP, your latest post is correct, it's the total wattage (VxA =watts) or power is the critical thing for fuses or circuit breakers, so voltage is just as important as amps.
Anyway, the mystery of the circuit breaker on the light switch is solved. They're removable, so I can switch them out. The picture is the two side-by-side with the rating markings on them, so clearly the manufacturers understood the importance of power capability for them. The shiny one on the left is from the 12V switch and the one on the right is from the original 6V switch (took a little cleanup to reveal the rating). 20A at 12V versus 30A at 6 V. Not identical power, but definitely different amp rating.
The only outstanding issue is if the dimmer will work correctly. I'm going to check them and if the rheostat on the 12V switch is close in resistance range, it should work OK.
[On edit] The rheostat full resistance on the 6 V switch is ~5 ohms and on the 12V switch, ~10 ohms, so the only thing that will happen is the instrument bulbs will be able to dial down to a dull glow.
FYI, the fuse out of the feed wire to the turn signal switch on my truck is marked 25A 32V (which is strange).
And yes, I'm an Engineer, but Mechanical, not Electrical. I know enough electrical stuff to be dangerous.
Which is why I ask questions.
