On Tue, 22 Dec 2015 21:59:43 -0700, Tony Hwang
wrote:

mike wrote:
On 12/22/2015 6:08 PM, wrote:
I have a farm tractor with a positive ground. I hooked a 15A battery
charger to it, and had massive sparks shooting all over the place. Yes,
I did connect the polarity correctly, with the red clip on the batt +
post and black one in the batt - post.

Because of this, I removed one of the battery cables (to the
tractor)[the negative one], and reconnected the charger. The sparks were
so intense, they melted a small hole at the top of the battery post.

In all the years I have charged auto batteries, I have never had this
happen. Even touching the clips together on the charger dont cause such
intense sparks. What the heck could cause this?
My first thought is a shorted battery, but the tractor lights work fine.
There just is not enough charge to turn the starter over fast enough to
start the engine. I would think that if the battery was 'dead shorted'
it would not operate the lights, or make the starter turn slowly.

To insure the charger is not defective, I connected it to another
battery and it's charging properly, on both the 2A and the 15A settings.

Anyone have any clue what's happening. I sure dont!!

Did you actually measure the battery voltage??
If you have a GENERATOR instead of an ALTERNATOR, it's possible for
the thing to get polarized backwards and charge your battery backwards.

Did OP put in a new generator then?
Not necessarilly. If the battery went dead at some point and it had
trouble charging someone may have "flashed" the generator in reverse
so although it LOOKS to be pos ground it could really be negative. He
needs to test with a voltmeter to be 100% sure.