Great information Greg!
When doing a diagnostic check, as is the case here, I always start at the fuse panel. Turn the key to run, or on position, and with a volt meter (one probe of meter to fuse, the other to a good, clean ground) check BOTH sides of every fuse in the block first. This ensures me that 12 volts is in fact making it to the switches, and then as Greg described above, go from there.
A fuse will usually tell you that you've got problems, meaning mis-wiring, by blowing. If no blown fuses, 99% of the time it is a grounding issue.
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