Johnson 88 outboard. How do you disconnect the lower unit to replace water pump?

remove bolt(or retainer depending on what year) on shift rod shift control box to ensure that rod is disengaged then remove 4 bolts from around gearcase flange the large 5/8 bolt above the prop area that goes up into the ex housing and the remove the trim tab and look up into the pocket and you should see another 1/2 in bolt going up into the ex housing as well if all original you should have removed 6 bolts then pull down on gearcase if you need to tap CLOSE TO CASE ON VENTILATION PLATE with a 2x4 or soft hammer to lossen gear case it should come free some times they get stuck from people not greasing the drive shaft splines or salt water corrosion MAKE SURE YOU GREASE SPLINES BEFORE REINSTALLING GEARCASE

on one side of the motor, probably the starboard side, about halfway up there will be a small rectangular plate with a screw at either end.

its an access plate to where the shift linkage on the lower unit connects to the linkage on the motor.