12 volt conversion on 1940 Desoto Coupe

[40desoto]

Beginning the process of converting to 12 Volt. Everything on Car is original as far as I can tell. Straight 6 flathead. (not sure of size because I cant decode numbers)

Can someone please guide me as to what I would need to convert or change on the engine to get it started with a 12 volt. I dont care about the lights and guages for now but more interested in the Coil, distributor, etc..

I know I will need to change over to a 12 volt alternator, and I head I can keep the same starter.

[james curl]

You will need a 12 volt starter relay to replace the 6 volt now in use, a ballast resistor for the coil, wired, 12 volts to start then 6 volts to run. I have used my 6 volt starter on 12 volts since 2006 and I generally drive it four or five days a week around town.

[greg g]

Lots of discussion of cneverting 6V+ to 12V- us the search function. But whay the need for conversion, are you going to be loading it up with recievers, amps, GPS, etc?

A well maintaned 6V system will work just fine, the did 60 yeas ago they still do today.

[40desoto]

You will need a 12 volt starter relay to replace the 6 volt now in use, a ballast resistor for the coil, wired, 12 volts to start then 6 volts to run. I have used my 6 volt starter on 12 volts since 2006 and I generally drive it four or five days a week around town.

I turned it over with a 12 volt batttery and turned the engine right away and fast. I installed a new 6 volt battery and it only spun the started but not the engine.

Can I just change to a 12 volt negative ground coil instead of adding a ballast resistor?

[40desoto]

Lots of discussion of cneverting 6V+ to 12V- us the search function. But whay the need for conversion, are you going to be loading it up with recievers, amps, GPS, etc?

A well maintaned 6V system will work just fine, the did 60 yeas ago they still do today.

Yes.. I plan on customizing and adding stear and airbag suspension.

[greg g]

You change the leads on the coil so neg goes to the points, wire the ressistor between the ign and coil. no need to change the coil. Swap the leads on the ammeter also.

[Rusty O'Toole]

What are you going to do about the 6 volt transmission control system? 6 volt wiper motor? Heater etc?

Better and cheaper and easier to leave it 6 volt and fix what's wrong. You can fix the starter, it may only need the cable connections cleaned, or even if you need a rebuilt starter it will be easier than changing to 12v.

I have seen this question many times but have never seen one successfully completed.

[Adam H P15 D30]

Never seen one completed??? Really??? Let's see.... My 39 Plym, 12v for 5 years, that was 20 years ago. My 40 Ford pick up, 12v DAILY DRIVER Flathead 60k miles in 7 years. R10 overdrive adapted into the torque tube with 6v solenoids running on 12v for the duration, no problems. Sold it and it is still going. 49 Dodge, 12v for the last 3 years, weekend driver but no electrical problems.. All of my conversions took less than a week to COMPLETE. If you do electrical add ons, it is really ok to go to 12v to support them. Sheesh

[Robert Horne]

On my 38 Coupe I have been running 12 volts about 20 years now.

I installed a 12 volt generator, 1956 model. The starter was 6 volt for

many years, but now a 12 volt starter, 1956 model. I never changed the

distributer. I did clean the points this summer.