Do you know which wire from the ignition comes from the positive side of the battery? You should branch off another wire from it to a separate switch for the lights. If the 420 wires up like the 212, it shuts down by grounding out the coil, not by running the battery power to anything in the ignition system. If you have a relay that's fired constant hot from the ON position of the ignition, you can branch off of the relay to get a constant battery voltage to some lights while the key is ON. Just remember that the battery voltage is for starting and charging circuits. You can't run lights off of the wire going to the starter for sure, and you just need to use a meter to find what wire gets that constant positive voltage when the key is ON. Even the cheapest volt/ohm/meter will let you find that stuff, just don't use it for any voltage that can kill you. Get a real meter for that.