i hooked my battery up backwards once and it killed the battery. what did the voltmeter say? a good battery should read close to 13 volts, not 12. that still does not mean it has enough amps to turn the motor over. when you push the start button, it makes the starter selenoid create a connection from the battery to the starter. while you have your ebox open, you can take a screwdriver and cross the two large posts on the starter selenoid. this will send power straight from the battery to the starter. if it doesnt turn the motor over, your battery is bad. if it does you have a bad selenoid or starter switch/connection. either of which should not be affected by connecting the battery backward. also remove your plugs so that there is no compression and the motor will turn over easier. oh and if you ever turn your motor over with the plugs removed the plugs need to be in the caps and grounded so they spark or you could damage your CDI.