Check the breaker for the cabin lights
Check volts at the output of that breaker
Also check to see if everything else still works
If you have to get into the wires, start by taking down the first figure closest to the breaker panel and check the voltage. Usually that light will feed the other more distant lights.
All of your wire connections should be at a fixture. Really bad hack job if wires are spliced in non-accessible areas like behind head liner.