No power at ignition switch.

In my experience, sparking or arcing when installing something in a live circuit usually leads to a blown fuse or tripped circuit breaker. Whether messing around with house or car wiring. Having no power after that is a dead giveaway. I doubt mechanical connections are going to suddenly go bad if they were ok before that.

If that happened to me the first thing I would think of checking is the fuses in the fuse box.

Next would be the fusible link which looks pretty much like a wire spliced into the loom in the vicinity of the bulkhead connector. It acts like a fuse because it is a smaller gauge wire that burns out when overloaded to save the main wiring and hopefully prevent a fire.

You can also check the bulkhead connector that passes through the firewall. (Looks like a rectangular plastic block on the firewall with a bunch of wires going into it to the left of the master cylinder) The contacts for the heaviest black and red wires are notorious for causing problems as they were not the best choice to carry that much power. As they age and get dirty, the resistance goes up and generates heat which melts the plastic and wires. You can carefully unplug the engine side of the block and inspect them in both halves of the plug.