The Dell CPU fan connector is J1F1. Using a voltmeter, I was able to measure the voltage at the pins with respect to ground, and figured out how to connect the fan.
You need to pay special attention to the tachometer signal pin. If it is incorrect, Dell motherboards produce an error message upon boot up. The message is Previous Fan Failure.
There is a BIOS option to bypass this message permanently by setting the 'Keyboard Errors' option to 'Disabled'. This normally does the trick.
Another method to eliminate this error is to use a 1 kO resistor and solder it between the yellow tachometer sensor wire and ground.
The diagram above is the J7J2 connector pinout
This Article Continues...Apple G3 to PC Modification
Inside The Apple G3 Case
Apple G3 Disassembling
Removing Apple G3 Motherboard Standoffs
Making a 20 Pin Molex Extender
Apple G3 with Dell Motherboard
Floppy Drive and CD-ROM Cage Mod
CPU Heatsink and Cooling Assembly
Dell Motherboard Connectors J1F1 and J7J2
Final Results: G3 is now a PC!