These VSSBs have been modified with 6 pin DIP switches to enable calibration for different tire sizes and gear ratios.  This style works with '87-92 style ECMs like the 1227747, '91-93 1227060 and the '93-95 16197427 or equivalents, instructions are included.  They work great with our TBI harnesses that have 700R4/ 4L60E/ 4L80E transmission control.  If your setup has the DRAC built into the gauge cluster, this probably isn't a good replacement.  These work with all of our TBI harnesses that have VSS wiring.