You can choose a handful of wires to splice into for adding a switch. If you want to add a fuel pump rewire harness upgrade, it would make this even easier to work, using the new relay trigger wire that won't disturb any fragile OEM wires. This way you add a nice upgrade while keeping the change reversible and simple to reach (comes from trunk, which is even less expected).
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On a friend's Camaro, I just got into the ignition wiring as it approached the firewall behind the dash, and did some creative routing to appear stock, until it split off to the switch location.
Watch some videos and read around the internet to collect some ideas from various communities, and get a good idea of what you want to do/where you want to route things.

GTP Fuel Pump Hotwire Kit
GTP Fuel Pump Hotwire KitThe Fuel Pump Hotwire Kit allows you to replace the stock, inadequate 18 gauge wire with a new 12 gauge feed using all OEM plug and play connectors! No wires to cut! This kit will increase the voltage at the fuel pump on average 2.5 volts. Make the most out of your aging fac

On a friend's Camaro, I just got into the ignition wiring as it approached the firewall behind the dash, and did some creative routing to appear stock, until it split off to the switch location.
Watch some videos and read around the internet to collect some ideas from various communities, and get a good idea of what you want to do/where you want to route things.