The amp load on the alt is causing the RPM drop and belt squeal. Dodgy wiring will add resistance to the circuit, which reduces current and therefore reduces load on the alternator. From the pic in post #29, your wiring is dodgy.
Fixing the wiring could actually make the problem worse since letting the fans draw more current will load the alt more.
If the harness is pretty stock, you might look into new engine harnesses. They aren't too much money.
I'd be checking for hot spots in the existing wiring when the fans are on, as well as how they're wired. Maybe run them off relays fed closer to the battery, which can provide far more current than the alternator.