The original blower switch was riveted to the lever assembly. I would be amazed if yours was still original. They last a shorter and shorter time as the blowers get old and draw to much current.
They fail because the mmetal contacts get so hot they melt their way into the plastic backing releasing the tention on the contacts increasing the heat untill they don't work.
I have probably diagnosed that system a thousand times and wouldn't think of doing so without a wiring diagram. What is really confusing is that the switch works differently depending on whether you are in A/C or heat mode.
Bosch Master, ASE Master, L1
33 years MB technician