The 1988 Jeep Cherokee, Comanche, and Wagoneer 4.0L engine series use an auxiliary fan. The auxiliary fan is controlled by a relay mounted on the left inner fender panel. When the A/C (if equipped) is turned on, the Electronic Control Unit (ECU) grounds the A/C relay coil allowing current to flow through it. This activates the A/C relay which then supplies current to the A/C clutch, fan diode assembly and cooling fan relay. Find more information about 1988 Jeep Cherokee Engine Cooling Fan Circuit and Wiring Diagram here