I just re-installed my 4.6 northstar after repairing head gaskets. Im stumped as to where a paticular line goes. Coming up with the fuel lines into the engine compartment is a 3rd nylon line that has a rubber boot on the end such as a vacuum line would have. Where does this go? Ive search my repair manual to no avail. Theres not much slack in it so it cant be far from where it is.. Book looks like it show it going to TB but i dont see any port on there for it. Thanks for the help.

?? Model Year ??

96 cadillac eldorado etc

Your 3rd line is probably the EVAP system plumbing that will be connected to a valve that should be mounted on the firewall side cam cover between cylinders 1 and 3.