That is a commonly asked question.

Stovebolt Tech Tips (in menu near top of this page)
Electrical System section
12v Conversion
https://www.stovebolt.com/techtips/12_volt_conversion.html

I like this style/configuration reducer:
https://www.classicparts.com/1947-54-Gas-Gauge-Voltage-Reducer/productinfo/24%2D995/

When you have some spare time, Check out the extentive list of Tech Tips (actually, in your spare time, check out the list of TechTips every so often).