There are numerous tech. articles out there that cover this issue. When you switch from the stock FI to carburetors, you have to install a low pressure carb fuel-pump, but since the FI fuel pump is controlled by the FI brain, removing the brain means the wires to the fuel pump won't give you 12V to the stock fuel pump connector.

There are a lot of "band-aid" solutions out there, some people remove the fuel pump relay and add a jumper there, others even run the pump off the coil! While all those solutions work (more or less) they all lack one thing, you're now running the pump without a relay! (and in case of the coil, without fuse as well)

The best (and also easiest!) solution is to trick the relay board into believing that the FI-Brain is still connected ...
This install is clean and simple! (and cheap!)

It's as simple as connecting one wire from the 4-prong FI connector to ground. You keep the stock fuel pump relay and fuse and you use the stock wires to power the new fuel pump. Below you'll see pictures showing how to attach the wire.
The thick red wired replaces the FI-Brain ...

On the pump side, simply make 2 more extension wires with "male" connectors on one end and plug them into the stock (roundish) plug for the stock fuel pump. There is no need to hack into the original harness.

Power Supply and Fuel Pump Relays must be installed

In order for this modification to work, you must have the power supply relay and the fuel pump relay installed in the relay board. These can be seen in the relay board picture below. If you removed these because you preveiously were powering your fuel pump in some alternate method, you will have to reinstall these relays. You need both because, the power supply relay powers the coil of the fuel pump relay.

Locating the Factory Wires

If you no longer have the factory fuel pump connector or a PO has cut the factory fuel pump wires, you can still use this modification once you locate the factory fuel pump wires.

The original wires on the later models (75-76) run up through the center tunnel and terminate under that gas tank where the FI pump was mounted.

The original wires on the early models (pre 1975) run over to the passengar side engine shelf. They are initially bundled with the red wires that run to the battery. They split off and drop through a round hole where the engine shelf drops down in the "hell hole", next to where the mounts for the original early fuel pump are located. The mounts are on the bottom side of the engine shelf. There will be a round connector with 2 slots in it. This is the connector for the original fuel pump. You may be able to see this connector dangling if you crawl under the car and look up just a bit forward of where the battery is.

The actual wires running to the original connector are a brown (GND) and Black with red stripe (+12v switched via fuel pump relay).

If the original wires have been cut/lost/removed, you can pick up the fuel pump +12v signal from two places on the relay board.

The +12v wire is a black wire with red markings that connects to Pin 13 of the flat 14 pin connector (T14) on the relay board up by the firewall. This connector is the one closest to the driver & front of car. Pin 13 is the pin closest to the driver side front wheel.

Alternatively, this signal was also routed to a white wire that attached to Pin 12 of the flat 12 pin connector (T12). This connector is on the passenger side of the relay board. Pin 12 is the pin closes to the passenger side rear wheel.

Last Resort & Dedicated Power Circuit

As a last resort, you can pick up a NON-FUSED switched +12v signal from the T4b connector. Pin 1 will be +12v whenever the ignition is on. It is a private circuit that is powered by the power supply relay which only powers the fuel pump relay coil and Pin 1 of T4b. Pin 1 is the pin closest to the passenger side front wheel.
WARNING: THIS PIN IS NOT FUSED and should only be used if you are unable to use the factory fuel pump relay and wiring or if you want your pump on a dedicated circuit seperate from the rear window defroster and heater blower motor which are shared by the factory fuel pump circuit. Please use an in inline fuse if you chose to get power from this pin. If you do decide to pull fuel pump power from this pin, the power supply relay will be supplying power and the fuel pump relay will no longer be needed. You can either pull the fuel pump relay or keep it installed and use it as a place to store a spare relay.

See Relay Board picture below.