Electrical 94 Gt Headlights not working

The wiring pigtail at the headlight switch is suspect. Did you happen to inspect / replace that when you did the switch?

Sure thing, it's a common problem (melted wires and terminals) so pigtails are available for relatively low cost all over the web.
Could definitely be something else, but as you mention the headlight switch had things working for a while, it's worth a shot to check how that's looking.

https://lmr.com/item/WPT165/94-04-M...MIvoH7vqKA4QIVFFqGCh1T-QvREAQYASABEgIgo_D_BwE
1994-2004 Mustangs had a common problem where the headlight wiring over-heated during continual use of the lights. This overheating issue cause the plastic plug to melt and malfunction. If this has happened to your SN-95 Mustang, LRS has a repair harness for you. This is the square plug that fits into the back of the headlight switch. It comes with 6 inches of wire pigtail that makes it easy to splice into the factory harness and repair your damaged plug.