Okay, this thing is kicking my ass. I unplugged the relay "socket" so I can look at the terminal numbers on the relay itself. I wrote down which color wires off the socket went to which terminals on the relay itself, to make wiring things up a little easier for me. But I realize that saying which terminals went to which functions is a better indicator of what I did, instead of wire color, so here goes.

Attempt 1:
30: output to fan
85: to 30A switch with LED indicator
86: to ground
87: to battery positive (30A fused line)
Result: nothing, switch did NOT turn the fans on

Attempt 2:
30: output to fan
85: to battery positive (30A fused line)
86: to ground
87: to 30A switch with LED indicator
Result: same as 1

Attempt 3: this is the wiring diagram on the relay "socket"
30: output to fan
85: to ground
86: to 30A switch with LED indicator
87: to battery positive (30A fused line)
Result: same as 1

Attempt 4: this is the wiring diagram on the relay itself
30: to battery positive (30A fused line)
85: to ground
86: to 30A switch with LED indicator
87: output to fan
Result: same as 1

I then installed a fused line with a 25A blade fuse for the switch, and repeated all four diagrams above. Then I removed the relay socket and ran wires directly off the relay terminals, and got the exact same results, switch did not turn the fans on. Then using black as ground, I attempted every variation of wiring combinations I could think of with the three remaining wires, and got nothing. It's a good thing I'm taking medication, because I'm ready to rip these fans out of the truck and smash them into a million pieces...

Is it possible that the relay itself is bad? How can I test that (my test light doesn't work, but I do have a multimeter)? After every wiring attempt, I then jumped the fans and the switch to the battery, and they both worked, so it's not those components. Again, by process of elimination, it has to be the relay?