MTFCA Forum

Last (hopefully) ignorant questions. I bought this car from a guy who picked it up from a family who had an older gentleman who had it and he passed away.

My 1927 Coupe has a positive ground, 6 volt battery (yes, I checked the ground). It will only charge to 35% and is very weak.

First question is what battery should I replace the battery with? There is currently a Die Hard battery in the vehicle and it is a 6 VDC battery.

Second question is since I am trying to upgrade the vehicle, should I go ahead and change it to 12 VDC, and if so, should I change it to a negative ground? I have already upgraded the headlights and bulbs to 6 or 12 volt LED lights that says are either positive or negative ground. There is a kit to change the voltage on the car, but there is some question about the starter operation under 12 VDC.

Your opinions are greatly appreciated.

The car is supposed to be 6 volt negative ground. I would not convert the system to 12 volt. You will need to re-polarize the generator before running the car with the new 6 volt battery and be sure to connect the battery correctly. If you want to run 12 volt accessories, 6 to 12 volt converters are available at low cost. Using one of them to power 12 volt items avoids the expense of changing everything else on the car. The original starter, magneto, and buzz coil ignition work very well. Excellent 6 volt LED headlight equipment is available. PS: Cheap batteries are cheap for a reason. Buy the best battery that will fit.

TXGOAT2 wrote: ↑

Mon Aug 25, 2025 6:46 pm

The car is supposed to be 6 volt negative ground. I would not convert the system to 12 volt. You will need to re-polarize the generator before running the car with the new 6 volt battery and be sure to connect the battery correctly. If you want to run 12 volt accessories, 6 to 12 volt converters are available at low cost. Using one of them to power 12 volt items avoids the expense of changing everything else on the car. The original starter, magneto, and buzz coil ignition work very well. Excellent 6 volt LED headlight equipment is available. PS: Cheap batteries are cheap for a reason. Buy the best battery that will fit.

I am told that to re-polarize the generator, I will need to install the battery with negative ground, then use a jumper across the terminals on the generator and touch them in several short intervals. Is there an instruction for that?

Thanks for your help!

Mike

Hi Mike,
To help lets get more info, have you had the car running? are you charging the battery with a charger or with the generator? any chance the
cables accidently were switched? The battery should have a group # on it. Do you have ready access to 6 volt batteries? How are you testing
the battery state of charge? Not knowing anything about the starter I would not chance going to 12 VDC. I'm sure someone can address the
reversed polarity it seems to me that has been discussed more than once on the Forum ( I think that is a model A guy thing ) converting to 12 VDC
has as many down sides as up sides but dos work in some situations.
Craig.

If the battery is in the stock position (in the trunk), it would take a Group 1 battery but it most likely will be too low in the carrier - all the vendors carry a battery board to get it up to the correct height or close to it ! Keep it 6 volt & negative ground - musta been owned by a Model A guy !

RajoRacer wrote: ↑

Mon Aug 25, 2025 7:30 pm

If the battery is in the stock position (in the trunk), it would take a Group 1 battery but it most likely will be too low in the carrier - all the vendors carry a battery board to get it up to the correct height or close to it ! Keep it 6 volt & negative ground - musta been owned by a Model A guy !

No, it is under the seat in a recess area which appears to be original and has a board floor.

The closer to standard configuration the more help you can get, without having to work around differences.
As stated, the T is 6 volt negative ground. !2 volts will be hard on the starter motor, so stick with 6 volt. 12 volt gizmos are add ons. If they fail you are still able to go down the road.

Allan from down under.

You must have a MODEL A !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Post a photo, please !

Make certain the battery cables are large diameter and not skinny 12 volt cables. Makes a big difference in starting and in charging the battery properly. Just went through this on a model A. With a new good battery, good stater and switch and proper cables, you’d swear it’s on 12 volt but not! And depending on how much you drive, a good quality low amperage battery tender helps. I just 6 years out of a 6 volt battery and I firmly believe it was because of the .08 amp maintainer!

Mike S. ..... Ford put the battery in a carrier frame that spanned the long frame rails with accessibility thru the trunk in the Coupe and Runabout.. ... Negative ground..... 2/0 cables...... How old is your Die Hard 6 volt battery ?.... Group 1, 6 volt battery.

Mike S wrote: ↑

Mon Aug 25, 2025 6:30 pm

Last (hopefully) ignorant questions. I bought this car from a guy who picked it up from a family who had an older gentleman who had it and he passed away.

My 1927 Coupe has a positive ground, 6 volt battery (yes, I checked the ground). It will only charge to 35% and is very weak.

First question is what battery should I replace the battery with? There is currently a Die Hard battery in the vehicle and it is a 6 VDC battery.

Second question is since I am trying to upgrade the vehicle, should I go ahead and change it to 12 VDC, and if so, should I change it to a negative ground? I have already upgraded the headlights and bulbs to 6 or 12 volt LED lights that says are either positive or negative ground. There is a kit to change the voltage on the car, but there is some question about the starter operation under 12 VDC.

Your opinions are greatly appreciated.

After reading through you description and the responses
Model A's were positive ground and the battery location was under the front seat. So as suggested some photos will help.
Its my understanding that a Model T Starter can run on positive ground without modification. But the generator and wiring need modifications.

Regardless of it being a Model T or Model A changing from 6v to 12v needs some justification. Why would it be necessary? So the question is, what upgrades do you have in mind.
A stock T or A doesn't demand much from coils & lights. In the past brighter headlights had higher amperage requirements & drove a variety of solution. With the latest "self focusing LED" headlights the amperage requirement is easily met with the stock 6v generator. Some note that running a 12v vs 6v gives better performance.

Standard battery size for an T or A is a Group 1 6v. There may be variations in specifications & price. A CCA specifications is for cold weather starting not so important for a T or A. RC, Reserve Capacity, & Ah, amp-hours are the more significant.

You will find many on here that advocate 6v and not 12. Its a hot topic comparable to water pumps, oil and distributors. Overall its a personal choice.

The primary argument for 6v is that it isn't hard on the starter. Of course how many are still finding an original starter they need to be easy on?

The primary arguments for 12v are convenient and ease of starting. Of course with a good clean system ease should become irrelevant, convenient is another. You just aren't going to walk into Walmart and find 6v bulbs, or a battery charger designed for 6v.

The generator will charge 6 or 12v and an original starter will turn on 12v fine. The weak link is the bending spring that can be broke if trying to start advanced. Battery cables and connections are a common problem with 6v systems.

It's your choice, I tried to give an objective view. I personally switched my cars to 12v for convenience more than any other reason.

I'd leave the car 6 volt negative ground. If you want excellent headlights, get the projector type lights that plug right into the stock T headlight sockets. If you want to operate digital doo-dads in your T, get a 6 to 12 volt converter for them. The converters are small and inexpensive and available in a range of capacities. The original Ford ignition system is fully adequate for all operating conditions and it offers several big advantages over "modern" replacements. The best way to upgrade a Model T Ford is to do what great-grandpa did, and trade it for a Model A Ford. Better yet, get one of each, and enjoy each for what it is.

The O.P. apparently doesn't realize he's not working on a Model T - they never had the battery placed in the cabin under the floor !!!!!!!!!

The Ford Model A came out in Dec 1927. You could easily have one of the first Model A's ever released. Picture Picture Picture

I have a 1930 Ford Model A coupe.The battery is under the floor and ahead of the seat, directly under the driver's feet. There is a metal access cover that snaps into the wood floor board. It is a 6 volt positive ground car. It has a belt-driven generator located on the driver's side of the engine. The same V-belt drives a water pump and fan. The car has a floor mounted gear shift and a regular clutch, brake, and a foot operated throttle. It has no reverse pedal.

“No, it is under the seat in a recess area which appears to be original and has a board floor.”


He has a T coupe, when the seat backrest is removed , you can access the battery, but same is easier to pull from the rear deck with battery strap. Was same on my ‘25 coupe.

T frames for battery have the frame bracket in same place.

He has what looks like a T from his older posts.

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