The main positive should go to the lug on the starter solenoid. There should be a couple of other wires connected to the same point, that power the rest of the truck.
The main negative should go to the frame; on my 88 it screws to the passenger's side frame rail a couple feet back from the front end. (The 88 and 92 have the same frame, but I don't know if it attached in the same place.) Before installing it, make sure that spot is clean, bare, shiny metal. You may want to sand or grind or take a wire brush to it, and then put a little "dielectric grease" (bulb grease or spark plug grease) on the frame, the mounting lug, and the screw.