2002

When the head light switch was replaced was there any evidence of over heating? Especially on the BN wire? Not a bad idea to test for head light on power at the head light BN wire.

Confirm that the interior Courtesy lights work when the dimmer switch is turned all the way up until the "click".

Confirm that the Instrument Illumination works. Confirm that the Instrument Illumination changes brightness when the dimmer knob is turned up/down.

Confirm there is power in and out of fuse F1.10, F2.19. Don't just "look" at the fuse. Use a test light that actually "loads" the circuit. Use KNOWN good ground.

IF this were my car I would use the test light to see if there's power at one of the front parking lights and/or the rear parking lights. Use a KNOWN good ground. Knowing the test results will give focus to further trouble shooting.

IF there's is CONFIRMED power with the parking light switch on, then look for a possible ground problem.

IF there's not power then we need to test for power at the head light switch BN wire with the parking lights on.

1999-2004 BJB CJB fuse panel layout:
https://www.allfordmustangs.com/for...r-swap-wont-fire-please-help.html#post2669271