2005 Hyundai Terracan battery not charging properly

Based on these measurements we are not going to be able to tell if the harness is the issue.

The only reason is, we don't know what the alternator is being commanded to do at the time it is producing these readings under load and no load.

The test that we need to do is check the wiring itself and see what voltage is required to get the current through the wiring.

That means we need to run the following tests. Refer to the wiring diagram but we need to check from the battery to the generator on terminal B. You do this by putting one meter lead on the battery terminal and the other lead at the alternator and see how many volts that wire is using. It should be very low. Wiring should not be using much voltage at all so if you have more than a volt then that wiring has high resistance.

You can do a resistance test that is shown in this guide, but voltage drops are a little easier because you don't have to take the connectors off to check the wiring.

https://www.2carpros.com/articles/how-to-use-a-voltmeter

Then you need to do the same tests for each wire on the alternator and let me know your results.

Thanks