I have a 83 ford mustang and i dont know where the return line goes ccan you send me a diagram of the fuel system

why?
ok the returnless system is totally differernt.
the regulator is in the pump and tank,
not knowing the reason, we can not help you,
running 2 pumps, huh? a lift pump and a pusher pump, what?
1: turbo added
2: for fun?
3: dont like loopless.

the stock system has a loop , its just dont leave the tank.
some cars have a mini tank near the fuel rail.
but most use the tank loop.
the pump is regulated then the return goes back to the main gas tank
immediately,.
the OEM Ford and others, puts a fuel pressure sender there.
because there is no vacuum regulator at the rail
the PCM then reads the pressure and adjusts pulse width to the injectors based on load .
The old system used vacuum to control the pressure directly
the new system Does not do that. at all.
there is no vacuum line going to the fuel tank
and at full throttle there is no vacuum at the injector tips
and as such will squirt too much fuel so the regulator drops the pressures about 6 psi. (from idle pressure)
see?
here is what needs to happen.
you just need a pump that works. and is rated for WOT fuel flow.
and the correct pressure set to factory spec, ford, pressure.
how.:
then use any manual regulator to set the pressure spec, pressure.
it never changes, then the stock fuel pressure sensor will report that
and the PCM does all the heavy lifting (calculations by magic)
that is how it works.

not knowing what you are doing so we can get on the same page makes all this impossible.
you are re-engineering the fuel system. so.... need to know that.

Im here,???
i want to go there. where and why.?
go to amazon dot com, type in greg banish books.
bingo read his books, (i have it on NOOK) for cheap.
it covers how loopless works and how it is tuned, to the finest details.

most folks down know why MPI systems drop 6PSI at wot.
it is because the reg is 1:1 reg for each pound of air pressure drop
so does the fuel pressure.
this magic on the old cars, keeps the differential pressure
ACROSS the injector the same at any throttle angle.
you car don't do that. at all. now.

and if you made it do that , id bet the PCM would go quite nuts.
it wants a static pressure. now.

no, clip the one purple wire.

http://www.autozone.com/autozone/repairinfo/componentlocations/componentLocationMain.jsp?fromSearchPage=true&categoryNValue=4294747011&categoryName=Fuel+Pump+Relay Here's a link to where the relay is and Iwill send another link on what it looks like.

This was the best I was able to come up with. Now there is the vapor/vacuum for the fuel system as well as vacuum lines for the A/C system but didn't know is you needed thoses as well. Hope these help.

I have a 2001 mustang gt with ac i dont have air comming out of the front vents so i bought heater controls and no difference then i found a yellow vacume line off but cant find where it goes can any one help me !!!!!! thanks mary

well i dont have a diagram but the run from the fuel tank along the drivers side frame to a frame mounted fuel pump then up to the engine. you can figure out what one is the return line by the fuel pump. the one that does not go to it is the sending not the return.

Did you do any tune-up?wires? coils?

I'd go back to the factory fuel pump, check the fuel cap too.

http://www.genuineservice.com/genuineservice/en/default?page=genuineService

Go to this website and pick owner guide on left task bar. Input your info and then pick owner guides.Your fuse information will begin on page 118.

There are lots of mustang "club" sites, google mustang club st. louis and away you go, I am sure you will run across someone that could expertly help you out.