What I mean is how/where did the fuel level sender wire exit the interior to go to fuel tank?
Do you have a picture?

 

The two wires from the tank went back to the left rear corner behind the bumper and were part of the taillight harness. There is a bulkhead connector at the back of the left quarter panel that plugs into the chassis harness, over the wheelwell, and runs along the driver's side rocker. You are probably familiar with most of this, but I included it for those that are new to these cars. OEM wiring was sketchy at best before all of the modern electronics were introduced.

 

None of this sounds correct/ stock.

The C313 was in use in 84 for certain.

 

Looks like even my 85 canadian lg4 (no computer or in tank pump) still used the c313, but with one terminal plugged.
Though i wonder where the brown wire leads to in the interior side.....

 

That brown wire in an EFI car normally would come from the C100 connector. Perhaps the wire is laid in the interior of your car and terminated at both ends (C100 and C313 connectors) but goes nowhere on the outside of the car (engine bay or fuel tank)?

I have unused wires laid in interior for options my car does not have. They just dead end at an unused plug somewhere.

 

This was taken in 2004 when I started working on the rear suspension.

Notice that there is no C313 on the rear bulkhead of my 84 Z28. This car had the feedback carburetor and mechanical fuel pump on the block, therefore there was no electric pump in the fuel tank. I added the C3XX from a 2000 Camaro SS that the fuel tank came from because it also had the connector for the ABS integrated.

 

Yep, it worked.

Although I used the parallel splice instead of the butt splice so that all the wires are in direct contact.

Molex 8 AWG VersaKrimp parallel splice, crimped with a HX-50B hex crimper (also known as Grote Cub, and Toolaid 18840)

 

What is the reason to switch from a 3rd gen tank to the 4th gen tank?
I am going to replace my 3rd gen tank (been sitting for 9 years with fuel) if it is dirty inside.
if there is a good reason, ill switch to the 4th gen (if i can find one)
this is why im askin

 

It's plastic so it won't rust, it holds 2.5 to 3 gallons more gas, it has an integrated evaporative emissions/charcoal canister system so you can remove that stuff from the engine compartment, it has a way better fuel pump module system that keeps fuel in its built in fuel well at all times, it has a separate fuel filler neck that connects to the fuel tank with a hose instead of being a one piece tank and filler neck assembly making it a b*tch to get out and put in. It fits into a 3rd gen like it was made for it.

Oh and you can do a proper fuel pump access panel in the hatch floor to make swapping out the fuel pump module assembly later on because all the fuel lines and wiring connects right there on top of the fuel pump module.

 

You can squeeze dual 525 pumps in there. That reason among others stated is why I want to switch over to the 4th gen tank