It is difficult to test these out of the circuit, because an ohmeter is simply not accurate enough. They really need to be tested under load
It IS important to understand how they work The switch is actually SEVERAL switches in one box, and there are TWO power supplies
1...Headlights ONLY switch function. The headlights only are a completely separate isolated circuit in the "headlight switch" assembly. UNFUSED power is tapped off the big black ammeter wire known as the "welded splice" and goes to B1 on the light switch. When the switch is activated, it sends power to the dimmer switch and on to the headlights. That part of the circuit has a built in circuit breaker
2...Park and tail. The other sections of the switch are fed power from the fuse panel from the tail / park light fuse. When in EITHER park or headlights, the "tail" terminal is live. When in ONLY the "park" position, the tail and park is alive. The newer cars which had park lights alive in either park or headlights DID NOT USE the "Park" terminal. They were wired in with the "tail" circuit
THIS SWITCH SECTION ALSO feeds power to the dash dimmer control when in either park or headlights
The power for the dash dimmer comes from the park/ tail siwtch, goes through the dimmer, and feeds TO the fuse panel on the TAN wire. The small INST fuse in the panel then feeds off to all dimmer controlled lighting on ORANGE wiring.
THERE IS ONLY ONE FAILURE point for that section, and it is the dimmer itself. The dimmer is simply a wire wound rheostat, and if it's subjected to a shorting/ high current draw condition, it will heat up like a heating element and burn out. THIS IS WHY the INST fuse is so small.
Frankly you are on the wrong track. The failure is not the switches fault, and can only be caused by one thing..............a shorting condition or wiring hack/ addition that is causing high current draw in that circuit. Look up the correct size fuse for the INST fuse and DO NOT use a larger amp fuse.
About all you can do, I believe, at this point is to remove the fuse from the INST clips and jumper power in there from some other source, AKA a temporary toggle switch (fused) and figure out a way to monitor current in that circuit. You need to research and find out what IS ON that circuit, and I already gave you some ideas Figure a way to isolate them, remove bulbs, shake, wiggle wiring, make sure you have the CORRECT bulbs installed and look for added /hacks/ changes. Gauge panel, tach, etc
