I recently removed a switch from a '66 Grande and put in into a '65 1/2 ton.... It too was intermittant.. So what I had to do is disassemble it, easy to do but be attentive, removed the terminals one at a time, cleaned plus retensioned them.

 Also, clean the metal pins that they come in contact with. Mine were a little green with corrosion.

 When you assemble, apply a good dielectric grease when you have all the terminals in place........  

Thanks for the help. I will be adding my pictures and as much info as I can. I am new to this and hope everyone will be patient.