Using our ’89 Wrangler’s OBD1 MAP sensor as a guide, there will be three wires in the harness plug: a power in, a negative ground, and a signal out. The wiring colors and locations may be different, so with the key in the Run position and the engine off, unplug the harness and test for voltage with a multi-meter. There should be 5 volts at the power wire. If not, the problem is upstream of the MAP sensor in the vehicle’s wiring harness. Be careful with older plugs—the plastic gets as brittle as ice.