1991 Ford F150 Truck | Stereo Wiring Diagram 1991 Ford F150 Truck. July 15th, 2012 Posted in Ford F150 Truck. 1991 Ford F150 Truck Stereo Wiring Information. Radio Battery Constant 12v+ Wire: Green/Yellow Radio Accessory Switched 12v+ Wire: The stereo wiring diagram listed above is provided “as is” without any kind of warranty. Use of the information above is at your own risk. 1991 Ford F-150 OE Wiring Harnesses & Stereo Adapters Ford F-150 1991, 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.