If you're going to add electric fans then think about how you are going to run them.
If you are going to run the fans after the engine is shut off, then its best to have some sort of rewiring. A different wiring strategy is needed.
If they are only going to run when the engine is running, you can get away with a circuit on relays. Do it just like a headlight relay circuit.
The way to 'get away' with this will be by making sure the alternator chosen has the ability to produce enough power to run the fans, plus the engine's ignition, brake lights, and anything else electric needed at slow idle speed. The key will be ability to produce power at slow idle speed.
Alternator 'ratings' are always at some rpm well above idle. On top of that there's other games manufacturers use to pump up the numbers. What you will need to know is power (watts) or amps
at 14 Volts at idle rpm. Why 14 V? Because the battery is at 12.5 Volts (give or take). So if the alternator can't make the power at a Voltage above that, then battery is going to become the power source.
Here's an example of current flow.
View attachment 1715688895
In this example above the alternator needs to produce 31 amps.
By adding a second power distribution point to an auxillery relay/fuse box in the engine bay 20 amps have been diverted from having to go through the firewall.
