I have a 1991 F150 XLT Lariat 302. Need to know what the small plastic color coded lines between the back of the engine and the firewall behind the intake near the top are. They maybe two or three mm plastic lines...vacuum lines maybe? What are the pink and yellow lines? Does anyone have a diagram? Thanks!

Not sure, but they probably have something to do with your heating or A/C system.

The only diagram i found on this truck, shows the pink line goes to the solenoid bank, yellow to air cleaner, and red to distributor. The heater control line is black or white. Other black lines for map sensor, trans....ect. There should be, or was at one time, a diagram under the hood usually above the radiator. This is the one you should go by if its still there, the ones in the manuals arent always correct unless you have a book specifically for vacumn/wiring.