Rex Ryan Car Accident -- Smashes Red Mustang in 3-Car Pile-Up

Jets head coach Rex Ryan capped off his train wreck of a season with ANOTHER major accident last week in Pennsylvania -- this time involving his red Mustang and two other cars ... after Rex reportedly ran a red light.

Rex was driving along a road in Bethlehem, PA around 6PM last Monday when he allegedly ran the light and rammed another car -- which then crashed into a third vehicle ... this according to Deadspin.com.

According to the report, Rex denied to police that he was speeding ... but did NOT deny running the red light.

Police described the damage to all three vehicles as "moderate." There were no injuries. So far, no word if Rex was cited in connection with the accident.

It's unclear why Rex was driving around Bethlehem last week -- but there's talk he was in town to meet with the Jets brand new offensive coordinator Marty Mornhinweg (previously of the Eagles).