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 F150 Truck Car Stereo Wiring Schematic Whether your an expert Ford mobile electronics installer, Ford Racing fanatic, or a novice Ford enthusiast with a 1991 Ford F150 Truck, a Ford car stereo wiring diagram can save yourself a lot of time. Automotive wiring in Ford vehicles are becoming increasing more difficult to identify due to the installation of more advanced factory electronics.