MTFCA Forum

I just bought a 1915 and am trying to get it started for my first time. I have been told to install a battery in the back floorboard and I find wires already installed to connect to a battery. Problem is there is no indication of positive or negative on the wires. should it be positive ground or negative? thanks

Negative ground.
Trace the wires & figure it out. When you do mark your positive in red. Red vinal tape or shrink wrap.

A T with electrics is usually negative ground. However, it may make absolutely no difference which way you hook it up, depending on what the supply is used to power up. Without knowing this, the answer may be moot.

Allan from down under.

alexhouston wrote: ↑

Mon Jan 08, 2024 5:15 pm

I just bought a 1915 and am trying to get it started for my first time. I have been told to install a battery in the back floorboard and I find wires already installed to connect to a battery. Problem is there is no indication of positive or negative on the wires. should it be positive ground or negative? thanks

The simple answer : T''s were negative ground regardless of year. Making it positive ground just confuses people.

A better answer would depend on knowing what electricals it has headlights & taillights with a dimmer or maybe it has a starter, generator with cut-out or voltage regulator you have. A voltag regulator would dictate proper ground matching.
A wiring diagram for a non-starter is different than a later year with a starter .

What's your ignition switch look like
Also if just need a battery for headlights than a deep cycle battery is best. If for starting regular starter battery is more the way to go

Body style would help!

Larry -- Body style is irrelevant. As you know, all Model T's were negative ground.

Were not all early model T's magneto powered? Dry cell batteries were retro fitted to aid starting. Did it really matter if the dry cell was negative or positively grounded? If the battery power is to enable the use of electric headlights, the grounding can be either. It all depends on the application to be powered whether the battery needs to be negative ground. How that battery is fitted does depend on where it can be mounted within the body of the car. You can't hide it under the back seat in a roadster.

Without knowing what the purpose of fitting a battery is, and what car it is to be fitted into, we can only guess.

Allan from down under.

If the car has all the original 1915 wiring, eg no starter or generator, constant loss electrical system for the coils and lights, then you can safely hook it up either way... in fact, it's better for the points of the coils if you reverse it every so often. I'll even throw another ringer in here - if this is the case, and you normally run on mag, you can ALSO put a 12 volt battery in the car, as the coils will run just fine on 6V, 12V, etc... I had a Yuasa Motorcycle Battery in a (homemade) box under the back seat, all it powered was the coils for starting (since it's only for a few seconds it won't boil off your coil tar --lol--) and the brake light as it was brighter than 6V.

SAYING THAT -

IF you have a 1919-1927 starting and lighting system, then most DEFINITELY negative ground, as Ford did not do the positive ground thing until the Model A... ALL 1919-1927 Model T's that had polarized electrics (Starting and generating) were Negative ground from the factory. Also if you are running oddball devices such as a distributor and single coil (banish the thought ) that are polarity dependent (like modern stuff) likely you will also be - ground.