Drastius

I picked up a TPI fuel tank and sending unit for my LT1 swap, and put in a higher flow rate pump (for future mods).

I was wondering what exactly all four of the lines were four which come out of the sending unit.

The one line going to the pump is the discharge.

There is one line which goes down quite low, and almost touches the filter sock. I believe this is the return line.

The third line goes into the tank and is attached to some sort of filter/valve device. Is this a vent line? What do I attach to it?

The fourth line goes into the tank maybe a inch with no attachments. I'm guessing this is the evap emissions line. I have taken the canister out of my car so I was thinking I can block this one off.

My final question is, the original engine was a carburated 305 with fuel pump on the block. Three wires ran to the fuel tank. Will I have to do any wiring modifications, or will these wires supply enough voltage for the pump?

Project86Iroc

Its late, Im fuzzy, but here is what comes to mind. Your discharge comes off the pump. The return is mounted near the pump. There is an external vent that mounts right next to the tank on the chassis with a special vent/valve attached(Dont know exact function or if it can be substituted) and your evap. I wouldnt completely block the evap, you might want to just add a short piece of hose and some kind of filter. I know the tank is pressurized to some extent, so I wouldnt leave it completely open either.
AS far as wiring goes, the line should be battery voltage no matter what the application, and the sending unit should be the same as well. Now might be a good time to replace the relay as well
good luck with your swap!!
mike