WARNING: This page is about a different car, the 1994 Acura NSX and 1993 Acura NSX. However, it is still accessible from the selected car via links, so may be relevant.
This signals the ECM when the alternator is charging. See Fig 1
and Fig 2
.
Fig 1: Alternator (ALT) FR Signal Diagnostic Flowchart (1 Of 2)
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Fig 2: Alternator (ALT) FR Signal Diagnostic Flowchart (2 Of 2)