I have torn down a 1955 Custom Dodge Royal, with a 270 Super Red Ram Hemi, for a complete off frame restore. I am building it back as custom to suit my wants and needs. It had a positive ground 6 volt system. Right now the car is completely torn down and all old wiring has been removed. What do I need to do/buy to convert this car to a 12 volt negative ground system?

 

simply rewire it has negative ground

 

Start with a good harness that's easy to install - they don't come much better than a Painless universal. Some other companies ( and people ) will tell you different, but after installing four of this brand I conclude no one could make an "easier to install" more top notch harness. Switches in the car can mostly remain the same as most functions are turned on by making ground or feeding voltage. All other components should be of the 12 volt positive breed including alternator/generator and starter. You will have to explore any gauges though as ones that use 6 volts will be an issue using twelve volts and power seats and windows ( if you have any) as well as the heater motor and wiper motor could pose a problem. Lights shouln't be an issue but look closely at all sockets for polarity. My hat is off to you for undertaking this project and with a bit of research and patience I'm sure you will prevail. Good luck!

 

The essentials

Rewire as neg ground

Motors don't care about polarity unless they are newer PM magnet field (mini starters)

If you use the original ammeter, reverse the connections

You will need Runtz regulators for the original electric gauges, fuel, temp, whatever

You will need dropping resistors for other motors such as 6V heater, wiper. Follow the destructions. You may need more than one, depending on draw

6V starter would work

Use all 12V alternator, ignition, coil.

Obviously, change all light bulbs to 12V

 

Fixed your post. I guess that's your opinion, but frankly, I don't fine Painless to be much or any better than the competition considering DOUBLE the price!!!!

All of them in my opinion are poorly documented. NONE come with a diagram which actually details what happens in the fuse panel. At least a few circuits are poorly set up, IE going through the key accessory when they should not or vice versa.

NONE of them treat Mopars like they are "real cars." ALL are biased towards "GM"