95 taco 2.7 liter engine alternator wires (white, red, yellow)

Hi all, my neighbors 95 Tacoma 2.7liter engine with a new alternator doesn’t charge the battery. Output voltage from alternator is same as the battery (12.4)with the engine running. I checked the 3 wires going into the alternator with the ignition on and found, white wire has 12.4 v, red wire has 0 v, and yellow wire has 11.8 v. The red battery symbol is on all the time in the dash. Help me troubleshoot please.