Help! Honda Rancher 4 wheeler

I have a Honda rancher that I bought from my brother that was
in need of new brushes in the starter. I had it rebuilt at a starter
shop. I reinstalled it tonight and when I tried to crank it, I got a
spark at the battery and it shut everything down. I took it loose
at the battery and reconnected it and that reset the electronics
I guess because the power would come back on again to the
console but as soon as I hit the starter button again it did the
same thing. I took the wire loose from starter and checked with
a meter at the solenoid and at the connection. I have power to
one side of the solenoid and when I engage the switch, I have
power to the other side and at the end of wire so it seems the
switch and solenoid are working properly I assumed that the
starter was maybe grounding itself out so I took it out and
apart, checked the brushes and the terminal and all looked
good. I reinstalled it and it fired up like it should so I put
everything back together. As soon as I sat down on the seat
and hit the starter button again, it sparked again and shut
everything off again. I am very frustrated with this thing now
and don't know where to check next. Anyone have any
experience with these? Thanks

I have the same ATV, but never had a problem like that. The seat should not be an issue unless it is pinching a wire. I will keep watching your post.

A "spark at the battery" would indicate a loose/dirty/poor connection there.

Clean it up and tighten it up and give it another try.

Battery is clean and good tight connection. Have checked that several times. I don"t think the seat had anything to do with it. It worked fine until I spent all the time to put all the other stuff back on to cause a problem again. I am leaning toward something still in the starter because with it unhooked, I have 12 volts at the starter wire when the button is engaged

did you happen to also put a new battery in it?
I had 2 new batteries one after the other that had the same symptoms you describe. fully charged lights bright everything working touch the starter button completely dead. fought with it for hours looking for the problem even bought a second new battery. then I boosted with the old battery and it worked so put the old battery back in and still using it.
only thing I could think is the new batteries had a poor connection inside the case and when I needed current for the starter they disconnected give them a minute and you would have lights again. I sent them back for a refund.

On a Harley Hitachi starter if you put the brushes in wrong it will run backwards never throwing out the bendix drive.

Try doing a load test on the battery/connections. Put a test light across the battery terminals (the terminals coming out of the battery, not the cable connectors). Hit the starter, see what the light does.

If it goes off, the battery is discharged or bad.

If it remains bright, the battery is good, there is a bad connection somewhere. Start moving the test light down the line, move one end to the nearest connection (battery cable), leave the other end on the battery post. Keep moving it until the light goes off when you hit the starter. When it does, you have located the bad connection.

Check your ground also, I have a Polaris and a Can-am that the ground cable is always working loose on and giving me symptoms like you describe.

I had a very similar situation this summer, it turned out to be a broken post in the top of the battery. I bought a 5 year old Triumph from a private party and he had just put a new AGM battery in it. It was a little smaller physically and not secured so it was moving around in the box, and the cables are big and stiff.
I hauled it home and on my first ride when I pushed the starter button I heard a pop under the seat, and it was dead. If I would pull the battery post to one side then it was OK, The seller paid for a new battery, so all is well, and I secured it.

Don't care how many times you checked it, a visible spark at the battery is a BAD CONNECTION.

If the connection were good it would either work, or everything would dim out when you hit the starter and come back when you let off.

Are you saying it will start and run with the seat off when you are standing beside it? How can you see a spark sitting on the seat?

Like mkirsch said a good connection will not spark.
Pull apart and clean up your battery connections.
Tight is one thing clean and proper is another.

It had nothing to do with the seat...I was simply saying that it waited until I got everything out back together( air box, body molding, seat, etc.) to start giving problems again. Contrary to the expert with the attitude, it also was not the battery or connections. Problem was in the starter itself. A new one fixed it right up. Thanks!