Was new ignition-switch simply plugged in to fix? Or did you have to repair wiring as well?
U.S. Ninja 300s don't have immobiliser like European versions, so ignition-switch should be OK. It takes decades to wear out, so it's probably good.
Lucy brought up good point on fuses. Because you don't have dash lights when turning key ON, that's sign power isn't getting from battery to ignition switch to dash.
So you'll want to measure all fuses, including 30-amp main fuse on starter solenoid. This is ONLY way to determine if fuse is actually good. If I had penny for every time I heard, "fuse looks OK", but turned out to not conduct electricity...
here's how to use multimeter to measure voltage, resistance and current.
https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/all
And basic multimeter that'll get job done.
https://www.harborfreight.com/merch...buys/7-function-digital-multimeter-63759.html