[Jack21]

Petek is great with electrical issues.

The fan control relay takes power from the battery, through a breaker (I also like breakers better than fuses), and powers the fan. A control circuit turns the fan on/off based on the fan thermostat "completing the ground" when ON temperature is reached, and OFF when the water temp falls below a preset limit. It's also a good idea to include a manual fan ON in concert with the thermostat so the fan can be turned on manually. (I like having the fan stay on when I'm stuck in traffic on a hot day, so it doesn't cycle on and off). This control circuit carries just enough amperage to turn the fan relay on and off. Very little. If you're blowing fuses on the control side, check for shorts along the wiring length.

The only thing that uses electricity with the power off should be the sterio settings memory. Not very much. If more, you have other problems. A sticking alternator regulator leaving the alternator energized with the power off. (I used a Delco 12SI alternator to avoid this).