Older post, but here goes. On alts, volt reg's, battery. All cars. The battery pos is usually to the starters large lug and also goes to the main fuse box. And the alts, large lug. Key off power too. Key on power too only with the key on. 1 side always hot to fuse box. Key position on or off. Says power to something on other circuts key on. Not needed key off.
Routed to the voltage reg. There will always be a sensing wire. Sensing wire is sensing if the volt reg see's demand is from the batt or alt. The diff from the 2. I:E: batt is providing all the power to meet the demand, -> bad alt or reg. Working reg, see's the batt is taking more than it can. The reg increases the field on the alt to produce more amps, keeping the voltage around 13.5V What ever the amp draw needed.
When you went to the alts lug to power up the fans, you by-passed the sense wire.
How are the fans turned on or off? Temp sensor thru the radiator? Or on off switch?
If a sensor, get rid of the alt connection. Use a 30 amp relay from the batt pos to the relay input, inline30 amp fuse. Output from the relay, to the fans.
Switch or sensor to make it turn on or off. Batt pos, inline fuse around 10 amp inline. Batt feed volts to switch or internal electric magnet on the relay to close the contac to close and power up the fans. You are using low amp draw to control high amp draw to power up the fans. Hope this helps. Dave
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