Yes, it does have dash vents. We'll give it a try and see what happens.

 

Another thing to check... I seem to recall a ground problem with the tail lights on these trucks that causes the headlight wiring to get hot and melt the plug. at least on the Last 3 I have had this has been a problem. You could have a main body ground that has gone bad under the hood as well.

 

How about this one.... You state that when you re-install the switch shaft into the switch, out of the dash, it seems to feel 'right' with the two distinct clicks/detents. When the switch in installed in the dash the shaft feels different ? Sounds as if maybe the switch is not be properly mounted in the dash panel. I don't know how it couldn't be but stranger things have happened. The switch is designed with a tab so the it will only mount in the dash one way.

Have you tried the switch with the shaft re-installed in it without it being mounted through the dash hole. I would just plug the new switch (or even the old switch for that matter) straight into the wiring harness connector, install the **** shaft, and just let it simply hang from underneath the dash and see if things work any better that way.

Let us know, eh. Good Luck.

 

Mystery solved !!!!!Somewhere in this process I did check the fuse next to the flasher on the bottom. It looked good but I replaced it anyway. Sunday I unplugged a tangled mess of a trailer wiring harness, no change. Today I pulled the instrument cluster out and removed/replaced the plug for the dash panel. No change. Studied the wiring diagram in the Chilton book again and there is also a Brown/White wire to the plug that is hot at all times. This runs through the #4 fuse opposite the flasher diagonally. Checked #4, it was bad and under rated, a 10 amp in place of a 15. Replaced #4 fuse with a good 15 and problem solved..... finally.
I kind of feel like an idiot for not finding that earlier, but I do have a new switch and connector, and I learned how to pull the instrument cluster. $40.00 for an education and a $1.00 fuse, still not a bad deal. I didn't realize there were two continuous hot wires going to that switch... Now I know.
Thanks to all of you for your help and ideas. I was stumped, so was the guy at O'reilley's and my brother who is a mechanic by trade. He is the one that discovered the second hot wire. Just goes to show, you learn something new every day. I won't forget this one...lol. Thanks again everyone. BTW I knew it was in the dash right with the tang in the slot. The switch did feel right out of the dash unplugged, but was the same out of the dash plugged in. I did double check my installation because I thought about that too.