66 barracuda ignition problem

Maybe you need to look at amps, how many the alt' can produce and how many you are using in different conditions. A bound up wiper system can draw a lot of current, clogged or otherwise faulted heat/air system can too. Combined loads become overload so failure happens at the weakest link. Evidently the fusible wasn't the weakest link. We have to assume it will be eventually.
You might consider putting the headlights on relays to get that load off the failing circuit but that really isn't diagnosing and correcting.