Gas line leak. looking for a diagram of how gas lines are run

Only two are fuel lines, the main feed to the engine and the return line from the engine to the tank. One other gas tank line will be the EVAP line for sending gas tank fumes from the charcoal canister to the engine's intake manifold.
I think the other lines would be your brake lines to the rear wheels.

YouTube has many videos on repairing rusted fuel lines. Most people use the lines made of plastic in their repairs-takes special fittings though. These plastic lines have become very common now. In fact my '92 LeSabre has mostly plastic lines.

You either have a gas leak or a thief. Check the gas lines that run under the car and the connections under the hood

It depends on which one is leaking. You should have two fuel lines from the pump plus two or more lines for the vapor recovery. The lines for the pump are under 50-70 PSI.
I don't have a diagram.

There is no such diagram available. You will simply have to follow the fuel lines from the fuel rail on the engine along the truck frame rail towards the tank, or from the fuel tank along the truck frame rail towards the fuel rail on the engine. Some are on the left side frame rail and some are on the right side frame rail, depending on which engine your vehicle is equipped with. You simply have to LOOK.

More than likely you have a busted fuel line, or one of the connections from the fuel lines to the fuel pump is broken. If you know how to repair cars, drop the tank and find the leak. If you don't know how, have the vehicle towed to a shop. Driving the car would definitely be a fire hazard.

This sounds like you have a leak at the fuel pump and sender unit, either in the unit mount or in a fuel line. Check under your back seat for an access panel if you have one then remove it and look at the pump and sender mount to see what is leaking, you may have to start the engine to get it to leak as it may only leak under pressure, hope this helps, let me know

Evap cannister is located next gas tank . Sounds like vaccum leak problem with engine running open hood and listen for hissing noise in vaccum lines also crawl uder vehicle near gas tank and listen most of the time leak can be located like this.

You Will Need to Replace The Flex Hose & Or the "O" Ring inside it.

Sounds like the fuel pump. Its located inside the fuel tank so it would make sense that it only leaks when the truck is running. Hope this answers your question. Best of luck.
Greg

this suggests you have a fuel leak in the engine compartment. Possibly a leaking fuel manifold (injection rail), or the rubber line from the fuel tank is leaking where it attaches to the manifold. The fuel line to the cold start injector should also be checked. Rubber hoses on older cars become brittle and as they contract from very cold weather will leak. Turn the key to on for 1 minute but do not start the car. Then check under the hood for a raw fuel wet spot where the leak is.