+/- change
 

heres one for our electric buffs when changing from + earth to - earth should you swap the connections on the back of the gauges

Re: +/- change
 

and polarize the generator

Re: +/- change
 

Yes...Otherwise, your amp gauge will ready backwards...

Re: +/- change
 

AFAIK most pre 1950's cars had dashboard gauges that are not polarity sensitive. the only exception might be amp/voltage gauges (as previously mentioned) that contained electro-magnets (the poles would be reversed in the electro-magnet created if the polarity of the current that created them was reversed) but even then their needles would simply move backwards rather than forwards.

Re: +/- change
 

Yes, absolutely.

Re: +/- change
 

You did not say what year you are working on but the only gauge you need to change around is the amp. Most of the early years did not use threaded connections for amp gauges. You will need to slide the wire out of a loupe on the back of the amp and thread it in the the opposite direction. Use care to disconnect the battery first and don't damage the insulation on an old stiff wire.

Re: +/- change
 

to fordyford 39 fitted with sealy gauges

Re: +/- change
 

Some ammeters have terminals and some just put the power wire through the loop on the back (inductive meters). The solution is pretty much the same either way. Change the direction of the wire through the loop or swap terminal connections as applicable.

Radios may or may not be polarity sensitive depending on how the radio gets it's internal voltage changes for amplification. The old vibrators work either way but the solid state types don't.

The ignition coil is polarity sensitive as well. I don't think the King Seeley indicators care one way or the other.

Re: +/- change
 

1939 changed from amp gauges to VOLT gauges,1940 was also volt gauges.