MAX-TRAC was a traction control system that was way ahead of its time. It measured the speed of the left front wheel and compared it with the output on the transmission. If there was a difference, the ignition would short-circuit so the power on the rear wheels went down.
Because the system had lots of maintenance-problems and emission-control regulations would not allow to keep the system as unsophisticated as it was, it was dropped at all for 73.
Below you find a description from the 71 Buick brochure and from a 72 manual. The text in the brochure is nice: ".....a miniature transistorized computer actually compares the speed of the front and rear wheels..."