The way Jeep got different blower speeds was to interrupt the “high” speed setting with resistors. It is really easy to see here in this ’87-’90 YJ Wrangler upper plenum. This blower motor resistor can be found right above the passenger-side fresh air outlet inside the cab of the Jeep. Each coil is a resistor and “low” uses both coils, “medium” uses only one, and “high” bypasses the resistor entirely. In TJs, there are four speeds, but the same basic idea holds true. The loss of a blower speed almost always means that one of these coils has fried (much like a filament in a burned-out light bulb).