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On my 2001, V10 super duty there are 4 wires (red, green, yellow and black) coming from the wiring harness under the hood with the following tag attached."customer access circuits see body building book for installationinstructions". Wires ends are sealed at this end but are they connected to any thing on the other end? Assume they must go into the cab but could not find them.
The originally were probably red, blue (green), black, white (yellow) they probably faded. Under the dash you will find the other end of the 4 wires. They are pass through wires for running accesories through the firewall.
Sometimes it's easier to see them if you remove the fuse box. But you have to touch your nose or you won't see them.
They are usually taped to the harness that comes through the firewall. The big one, and right behind the fusebox. If you want to remove it, easy. Take out the 10mm bolts that you see and it will fall out.