The first thing to do in a case like this is to check, clean, and secure ALL connections in the battery cables.
Begin by disconnecting the battery negative cable from the battery first. This will safely de-energize the entire electrical system, this way you will not accidently arc a wrench and damage something.
Next, trace the battery cables to the starter solenoid, and then on to the starter, removing, cleaning, and re-securing each terminal connection as you go.
Then, trace the battery negative cable and do the same job on all its connections too.
The negative, or ground cables often get overlooked, but they are just as important as the "Hot cable".
All the above is really aimed at cranking circuits that have a separate, remote mounted starter solenoid, if your starter has the solenoid mounted piggy back on the starter, there is a different fix you may have to add to the cranking circuitry to get reliable cranking performance. Post whether solenoid is a separate component or if it is part of the starter on your engine.
And you might also post the actual model number of the Kohler engine, 19 horse is pretty useless, unless of course, you are a lawyer :^)

"19 horse is pretty useless, unless of course, you are a lawyer :^)" Gotta love it!
If you have a Courage, you could be dealing w/ excessive valve lash or a compression release problem. You could take a known good set of jumper cables and a disconnected known good battery and do a quick test. + to lug on starter. Touch - cable from battery and momentarily touch a good grounding spot on the engine. It will spark and the engine should try and turn. Let us know the engine specs and what you find.

Ok so its a Kohler Courage 18... dont know where I got 19 from.. Its like a year old or so and the cables seem pretty clean I havent had a chance to take them apart an clean yet ... thats my project on saturday. The battery was tested at autozone and they said it was good. Do you think that they may be wrong about the battery or do you think its something else.

If you follow the simple test outlined above you will be eliminating much of the guesswork. I encourage you to do so and post your findings. I'm not sure how we can form an opinion on whether or not your particular Autozone's test was correct. Or maybe it should go into the shop.

I have had the same ongoing problem for 3 years with a Troybuilt 24 hp with a 54" deck. It is in the shop again with another frozen clutch, also. I had it back for 2 weeks after $350 worth of repairs, including a new wiring harness. I charged that good battery 8 times till the clutch froze. Don't you think something is draining that battery?

Confused.

Here is a link that might be useful: Profile

Ok tried new battery. Testing the cables. Finally took it into repair shop they tore it apart put in new starter and a lot of other things. Got the Kohler rep out to look at it and it was a compression release valve. Luckily it was under warranty still. Now I am back in business!

Had to replace battery in Troybilt Bronco with 19 horse Kohler. I revirsed the battery, then tried to start tractor. After putting battery in the right way, nothing now works. Any idea what I damaged?

Well, the very first thing that might be wrong following a mix-up like that could be a blown fuse main fuse.
But a blown fuse may just be the tip of the iceberg regarding other things that might have been damaged due to reversed battery polarity.
Other damage may include the charging system diodes/regulator, so we'll have to take this a step at a time.
You did not state exactly why (symptoms) you had to replace the battery. ????

The old battery had went flat over the winter. Looked for main fuse, but couldn't find it. Have given up and having a repair shop look at the tractor.
Thanks for the advice,
Dave

***"Have given up and having a repair shop look at the tractor."***
Don't give up so easily.
Below is an excerpt from a Troy Bilt owner's manual (but not yours I bet cause I don't know your technical model & serial number) that might help you find the fuse (or two).
{{gwi:335251}}

Found 20amp fuse outside of battery box on left side from back of mower. Changed fuse, mower started, and runs fine.
Thanks for the Info.
Dave

Go ahead and take to a repair shop if it's gonna be all that complicated :^)

Magnets came loose from casing an cause one to break. I have had problems with the starter from day one. I called to order one as I need it desperately and found that they are back ordered in the hundreds. I am disabled and I need an answer asap. Thank you.