Charging Battery? Polarity?

[SteveAdventure]

I left the switch on and drained the battery in my 1928 JD. I thought I heard someone say that the polarity on these bikes was reversed! What the best way to charge the battery? Thanks!

[Sargehere]

No, J-models are NOT "positive ground," (like an old British sports car or such). The ground wire gets the black, (-) charger cable, and the hot wire (wired to the rest of the bike) gets the red (+) battery charger cable. Use a low-amperage, 6 volt charger, but not a trickle charger. No more than 2-4 amp hours, I'd say. Hope this helps!

[Randy STL]

Always look for the battery markings and connect the red battery charger lead to the battery (+) and the black charger lead to the battery (-). Never trust the color of the wiring leaving the battery, or which wire goes where.

Negative ground means the battery (-) is connected to the frame/chassis/earth ground. Positive ground means the battery (+) is connected to the frame/chassis/earth ground. This doesn’t change how you would charge the battery.

My JD had a slow battery drain and I tracked it down to the voltage cutout relay wired in reverse so that battery was always pulling in the relay. With the bike off, the top of the relay should be up. You can also verify that there is 6V across the cutout relay terminals when the bike is off, meaning that the relay is open and thus the difference in voltage. If the voltage is 0, then the circuit is closed. (Everyone does it differently - the other way is to measure each side with respect to chassis ground, in this method the battery side would be 6V and the other side from the generator should be 0V if the circuit is open)

Randy Hassler
#68 2012 Cannonball

[pisten-bully]

Sort of a hijack, sorry, but I ran into this the other day, a fellow I know put his 2008 BMW on the "smart" charger last winter, hooked up the leads wrong and the charger didn't react... until the battery drained to zero and then the charger began to charge. He claims the battery was then charged up with reverse polarity and fried his wiring harness when he keyed up this spring. I'm still doubting some of this story!