Blowing fuse when turn on running lights

It would be rare to be the switch.

WHAT YOU NEED to understand.......

There are TWO sources of power separately going INTO the light switch

One, unfused, comes from the ammeter "welded splice" is not fused and powers ONLY the headlights. The light switch has an internal circuit breaker for them

The second goes through the tail fuse and powers tail, park, and DASH lamps.

Very first thing I'd do is start to "simplify" the problem, and the very easiest way is to get into the left kick panel and separate the rear harness. In fact that is probably the most logical place for the short

If separating that connector does not eliminate the problem, go over the front lamps and harness, looking for damage. Examine the front marker lights, the park/ signal lamps, and follow the harness to the bulkhead connector. Look for melting, bare wires, evidence of physical damage