1989 Ford F-150 OE Wiring Harnesses & Stereo Adapters wwwd››Ford›F-150Ford F-150 1989, Aftermarket Radio Wiring Harness by Metra®, with OEM Plug. For aftermarket stereo. Metra preassembled wiring harnesses can make your car stereo installation seamless, or at least a lot simpler. 1989 ford f-150: harnessng diagram - the 5th wire is 1989 ford f-150: harness.wiring diagram - the 5th wire is orange - Answered by a verified Ford Mechanic. my 1989 ford f-150 radio/cassette has 5 wires in the power harness - 4 are identified by the wiring diagram - the 5th wire is orange/black - what is its function?