honda 2008 trx 420 rancher.

Just changed the starter and starter solenoid a month ago. The starter already sounded like a high pitch whining whenever you first start it. Didnt have any issues with it starting for about a month. Then all of a sudden it wouldnt shut off. You could turn the key off and even turn the emergency shut off switch and it would still crank. I had to take the negative pole off the battery in order to shut it off. Now when you touch the cable back to the post it will re-engage the starter even with the other switches turned off. I unhooked the starter solenoid to rule out the option of the solenoid being stuck on. The starter will still engage. Im not sure what the problem could be other than i just bought a bad starter.

 

"I unhooked the starter solenoid to rule out the option of the solenoid being stuck on. The starter will still engage"
This is impossible, if you disconnect the heavy wires to the solenoid there is no physical connection between starter motor and battery, so no way the starter is going to run with these heavy wires to the solenoid disconnected. The fault is the solenoid, but a bad battery can cause the solenoid to stick. If the voltage is a little below what it should be, it slows the solenoid down, and the contacts start to arc as they go together, and stick together once the button is released, but there are some bad solenoids out there too, so you could have bought a bad one.