I have a 1981 F100 and a digital clock from the same generation truck. There are two harnesses in the truck to the right of the heater controls, but neither will fit the one on the clock I have.
The wires on the clock are black, white with a purple stripe, light green, and brown. One of the two harnesses in the truck has both black and white with a purple stripe, but it also has green with a yellow stripe and blue with a red stripe.
I have really never done any wiring, and wanted to know how to connect the digital clock. Can I just cut the harnesses off and splice the wires together? If so, what do I need to connect the light green and brown wires to?