OK here are the pics. All four wires were disconnected from the small circuit board mounted underneath the lid. There are four wires: red, orange, yellow, black. The terminals on the circuit board are EIS 1, EIS 2, EIS 3, EIS 4.
I also want to verify that a shorter black wire mounts to the ground terminal on the back of the radio (as shown).
Cameron
1986 F-150 Base, 4x2, 4.9L I6, C6
1992 F-250 XLT, longbed extended cab, 4x4, 7.5L V8, ZF5 5-speed