Trailer ABS light in dash

This ABS Trailer fault light in the dash has been a requirement on all tractors since 2001.  The indicator lamp is used to alert the operator of an ABS fault.  The signal is a PLC (Power Line Carrier/Communication).

This signal is transmitted through the same ignition power (blue wire - pin 7 in trailer connector) used to power trailer ABS.  It runs at a different frequency than the power lead for the trailer.  If the trailer ABS unit fails, and has an active code, it stops sending the PLC message and will turn on the ABS dash lamp, if the trailer is wired to do so.  It does turn on the trailer left rear corner light (pictured) as well.  

For you non-drivers, were you aware of the purpose of that light in the picture?