Tail / Parking / Gauge Cluster Lights Not Working

Hello,

I'm currently experiencing a problem with my tail lights, parking lamps, and
gauge cluster illumination lights. None of these work anymore.

But here's the big mystery about this, of which I am unable to figure out...
Upon realizing that only my head lamps worked when operating the main
light switch (brake lights are also fine, and my truck does not have fog
lamps), I removed the switch and tested it out. All of the contacts were fine,
but there appeared to be a problem with the diode circuit for the 8th pin.
Therefore, I simply installed jumper wires in place of the switch, and sure
enough, everything worked. In my mind that probably meant for sure that I
had been right about the switch itself being bad.

Ordered a new switch, installed it, but to no avail. All lights except the head
lamps STILL do not work. I removed the new switch that I just installed, tried
the jumper wire trick again, and everything works. What I'm not
understanding is how it isn't a bad switch when I can make everything work
with wire jumpers in place of the switch?? Is it possible that something is
wrong with the dimmer switch? One thing I did notice during troubleshooting
was that the ONLY thing which did not work properly with the wire jumpers in
place of the main switch, was that I could no longer dim the gauge cluster
lighting. Is the diode circuit on the 8th pin of the main switch dependent on
another circuit somewhere else in order to be switched on to supply 12V to
pin 8 in the connector?

I'm extremely puzzled now, and if anybody has any insight as to what is
actually malfunctioning here, I'd very much appreciate the input.

Thanks,
Jim