Bad ground is the most common problem. When you push the button...can you hear the solenoid click? A 12 volt circuit tester light is a help for something like this. They cost about $2. Find out what wire is hot. And what terminals are a good ground.
Or maybe try connecting the battery negative directly to the negative wire from the motor. Usually the solenoid has a marking--a tiny S on one side for "switched"--this goes to the motor, and has 12 volts only when the button is pushed.
You can always bypass the switch with a jumper wire--making sure the motor and its ground is OK.