My wife has an 03 CBR600RR and somehow hooked the battery up backwards, I've replaced the 30A fuse in the battery box and the battery has 13 Volts but turn the key and no joy. I have checked the fuses on the left side and there all good but cant find any others, any ideas where else I can look?

 

to start with disconnect the battery and try another if you have one just to elliminate you havent naffed your battery,if the problem is sill there check the leads from your battery to the starter relay, this is the box the 30amp fuse was in,if you have a multimeter you can check the positive carries power to it and you can check the negative has continuity by checking it on the ohms scale, if this is ok next step is the relay its self,
hope this helps to start you off.