6V to 12V conversion advice

[JMFL36]

Update on the '54 Merc. I just ordered 3 Runtz Voltage Drops from Randy's 5th Ave Garage to protect the temp, gas and oil gauges. (https://www.fifthaveinternetgarage.com/electrical_parts.php#runtz)
I've disconnected the power leads to the heater blower motor, clock and radio for now. Next up is to troubleshoot the horns. Once I get them fixed I'm going to leave it as is until I decide whether to finish the 12V conversion the previous owner started or go back to a stock 6V system.

 

[dmsfrr]

If the Fuel and Temp gauges are working fine they shouldn't need the runtz regulators. If those gauges are like the Ford versions they work on heat & current flow controlled from bi-metal contacts in the sender. They aren't voltage sensitive.
King-Seely example diagram below.

 

[JeffB2]

Don't be surprised if you wasted your money on the runtz units. All you really needed was this for all three gauges. https://restorationpartssource.com/...1965-68-mustang-daniel-carpenter-details.html Ford used 6 volt gauges into the mid 80's with just this unit. You would wire it up just like the early Mustang.