Hello guys, hope yall are doing great!!

I need help with my 2001 Jeep Cherokee XJ Limited. I recently installed a 200-amp HD alternator to power two electric fans from a 2003 Ford Focus. I live in a very hot city with temperatures reaching 128.3°F, so the fans are wired to run constantly whenever the ignition is on. Previously, my stock alternator provided a consistent 12.5V. After the upgrade, the voltage remained the same. While troubleshooting, I discovered a missing ground connection between the battery and the frame. I added this ground and cleaned the other ground connections near the air filter, engine, alternator, and ground strap. I even added a copper washer to the ground strap.

Now, when I start the vehicle, the voltage initially reads 13.8V but then gradually drops to 11.98V. When testing the alternator without the battery connected, the voltage fluctuates between 13.2V, 12.8V, and then drops to 0V.

I'm unsure what went wrong. Did my attempts to improve the grounding worsen the situation? Or does the PCM require a tune/flash to work with the new HD alternator? Should I install an external voltage regulator?

Any advice or comments would be greatly appreciated. I rely on this vehicle to travel through the Baja desert and need to get it running properly 🏜️🌵🍻. Thank you in advance for your help.

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Check out Cruiser54 tips & tricks. Ground refreshing is for real.

 

Your running voltage has to be above the battery voltage to charge the battery. It occurs to me if your ambient temp is 123.3F, the voltage regulator may be reducing the charge rate , via the battery temp sensor. If that’s defective it could be part of it, or, your new 200a alt, I assume new, might not be working, ..many possibilities

 

You only need an external regulator if the new alternator doesn't have an internal one.