With a correctly wired system, any load placed on the battery will show on the amp gauge since the alternator is trying to keep the battery at full voltage. It doesn't matter how the accessory is wired up, if it pulls power from the battery the gauge will show it.
With the fan power feed coming off the alternator, it should not show on the amp gauge, it will go directly to the fan motor. This way, you're amp gauge will not show charge or discharge since the load is before the gauge. Not sure if its good for the alternator to work this way or not, but it would keep the amps lower through the gauge.
If you bypass the gauge you should at least install an aftermarket voltage gauge to keep tabs on the battery.
All accessories, ignition, lights, and what ever else you hookup, needs to be between the amp gauge and the battery. The alternator and/or generator needs to be on the other side of the amp gauge.
A single wire alternator ( self exciting ) is wired with the output lead directly to the amp gauge. The two wire is hooked up with main wire to the amp gauge and a trigger wire from the run circuit to alternator.
Your 14" fan will not take much power to run, just relay it off the battery with a toggle switch to turn on and off the relay, add an indicator light where you can clearly see it so you remember to shut it off when not needed. I would keep it high on the radiator and off to one side so it doesn't block air flow while driving as most in-front fan do. An easier method of cooling at idle is to simply increase the idle speed when its hot, an electric idle solenoid on a toggle switch would be easy to hook up and would increase the idle rpm a couple 100 rpm when needed. Or do as I do, when the temps start getting warm, I speed up the idle 100 rpm to compensate for the A/C, during the winter, I slow it back down.
