Welcome to iRV2 .
Freightliner wiring underwent a MAJOR change , Jan 4 1999, right after the Christmas shut down . Many 1999 coaches are actually on a 1998 chassis .
Can you find a decal giving the chassis build date , usually low on the wall to the left of the drivers seat .
BTW ; back in our chassis vintage , Freightliner didn't provide the trailer plug & wiring ; Newmar added mine.
Your wiring colors may differ from this diagram , but the function of each pin should be the same .