I just purchased a 1940 Plymouth sedan. Everything on it is 6 volt except the 12 volt elect. fuel pump that the last owner put on it. It has a 12 volt battery. What do I need to do to change to a 12v system? Can I put 1 step down some where in line, or do I need to put a step down for every gauge, lights, etc.....
Thank You.
Dan

That's positive ground 6v.. how is it hooked up now? pos or neg ground?

you need to step down the voltage at every gauge, and change every 6v bulb to a 12v bulb

How are you charging the 12V battery, has the generator system also been changed over. I think there are units that will step the whole system down. I would just wire the pump in ahead of the system somewhere.

Thanks for your replies. It is a neg. ground. Just found out today that the gen. does'nt seem to be putting out. Died when Battery was dis-connected. I am the second owner of this car. It was once a police car, the siren mount is still on the engine. I think it would be nice to keep it as original as possible, but I also want to avoid headaches down the road.
Any leads on who reconditions the gauges?

Years ago Ron Francis had some that would drop voltage to the whole dash instead of adding one to each gauge.

Here's one way to do it.

Get an old style 12V battery which have the bars on the top you can see connecting the cells and a 12V generator or alternator.

Drill a hole in the middle top bar of the battery and tap it. From that middle bar to ground in either direction you will have 6V. In other words, from the tap to the positive terminal will be 6V and from the tap to the negative terminal will be 6V. Hook up the alternator and battery as a 12V system and use the tap for powering lights, gauges, and anything else that needs 6V.

Note: You will probably need to rig a relay for the starter switch if it provides power to the cars accessories (likely) so that it sees only 6V and the new relay you install connects 12V to the starter relay.

If its anything like my 54 dodge you have 1 electrical gauge, the fuel gauge there are several drops for it, from the one for a ford gauge (this has been making my fuel gauge jump) to resistors. Rest are mechanical (oil, temp), or don't care (amp meter). Plus you probably want to get rid of the old wiring harness if its rotted at all or chaffed.

Also do you have electric wipers? And there are the fans. I'm probably gonna run mine on 12v, I have spare sets of fans, and will hopefully not use the wiper much. They have heavier draws and take different drops than the gauge, and most of those produce a fair amount of heat.

You will also have to step down the coil from 12v, or get a 12 v resisted coil/

Mine's still in progress, so I can't verify everything. Do a search on the forum there have been lots of these put out, my previous ones included.

Thanks To All Who Replied To My Question.
I Have Decided To Keep The 6 Volt Sys. For Now, But I May Change
Over To A 12 Volt Sys. In The Future. Thanks Again For All The In-
Put
Over The Hill