You need the kill switch to be able to shut the current off to the car so that means the big charge wire from the alternator needs to be routed to the battery side of the kill switch and then routed back from the switched side of that switch back to the starter relay feeding (charging) the battery off of the starter. I would replace the stock battery wire with a #8 or maybe even a #6 gauge wire depending on the amperage the alternator makes, 35 amp for 35 amps,or # 6-gauge for 60+ amps. The increase length of the charging wire comes into play so a lot bigger is better than a tiny bit to small
Have fun