If you plan to race this I don't think it will pass tech. Most sanctioning bodies require the disconnect switch to kill the motor and all elect. The simple solution is to run the charging wire from the alt directly to the POS battery terminal. Connect your junction box feed to the battery side of the solonid. Then place your cut off switch between the battery and the solonoid. That way when the switch is thrown ALL power is cut to the car. Battery and alternator.

At least this is what I have read on other threads. If I have this wrong I'm sure someone will correct me.