I have a 1988 Iroc that I will be installing a SBC 400 engine in it with a mechanical Holley fuelpump and would like to know if the Holley mechanical fuelpump will pull fuel from the tank through the pump in the take to the carb and which line is the output and return line(the bigger output or smaller return line)?THANKS

 

Probably not.

Large line is fuel supply, smaller is return.

I'd recommend using a Mallory 4309 regulator and the in-tank pump, instead.

 

Some say it will work with the Holley mechanical fuelpump and the thing is that when I got the 1988 Iroc it had no wiring harness so I got one from the boneyard and I cant get the fuelpump in the tank to come on.

 

I would not try to pull fuel through a dead pump. It's a restriction and you are cutting into the mechanical pump's fuel delivery capacity. I would either drop the thank and remove the pump and extend the fuel line pick-up (see sticky at top) or use the existing pump, see below

Here's the wireing diagram for an 88 TPI system

http://austinthirdgen.org/mkportal/m...ine_wiring.gif

Notice the fuel pump relay in the top half, center of the diagram. The Orange wire should be hot all the time and you should have the Tan/Wht wire going back to the tank. If you take the Dark Orange/Wht wire and temporarily connect it to 12 V you should hear the pump run. If that works, find a Pink/Blk wire and connect the Dark Orange/Wht wire to that. The Pink/Blk wire will only be hot with the key switch in the Run/Start position and that will keep the pump running.

I've seen some people use a timer relay in place of the stock relay to prime the fuel bowls and keep the oil pressure switch tied into the system. That way the fuel pump runs for a little bit at first and in case of an accident if the motor dies the fuel pump will shut off.