Re: 1941 instrument panel
 

If you want to go the Christmas light route, you can work out the voltage of the light string by adding up the battery voltage.

3 batteries (at say 1.5v each) is 4.5V. Two batteries will be 3v, etc. You just need to match the supply voltage to the batteries that came on the string.

When you are taking apart the light string, the battery pack may have a small voltage drop resistor in it. I replaced this (to get the correct drop for 12V), but if you can match the battery voltage, keep it.