Why is there no fuel to the fuel pump on my 1976 GMC 3/4 t Sierra 25 with S3 tank/ 2switch fuel delivery system and cruise control.

Why ? You won't fix it , take it to a qualified repair shop before mess it up.This vehicle has a fuel pump driver module (computer) that controls the fuel pump .
Fuel Pump Flow Control Module (FPCM)
The fuel pump flow control module (FPCM) is a serviceable GMLAN module. The FPCM receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The FPCM sends a 25 KHZ PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 15 amps. A liquid fuel pressure sensor provides fuel pressure feedback to the FPCM.
Electronic Returnless Fuel System (ERFS)
The electronic returnless fuel system is a microprocessor controlled fuel delivery system which transports fuel from the tank to the fuel rails. It functions as an electronic replacement for a traditional, mechanical fuel pressure regulator. A pressure vent valve within the fuel tank provides an added measure of fuel pump flow control module (FPCM). Desired fuel pressure is commanded by the engine control module (ECM), and transmitted to the FPCM via a GMLAN serial data message. A liquid fuel pressure sensor provides the feedback the FPCM requires for Closed Loop fuel pressure control.

Fuel Pump Flow Control Module (FPCM) - LMF
The fuel pump flow control module (FPCM) is a serviceable GMLAN module. The FPCM receives the desired fuel pressure message from the engine control module (ECM) and controls the fuel pump located within the fuel tank to achieve the desired fuel pressure. The FPCM sends a 25 KHZ PWM signal to the fuel pump, and pump speed is changed by varying the duty cycle of this signal. Maximum current supplied to the fuel pump is 15 amps. A liquid fuel pressure sensor provides fuel pressure feedback to the FPCM.
Electronic Returnless Fuel System (ERFS) - LMF
The electronic returnless fuel system is a microprocessor controlled fuel delivery system which transports fuel from the tank to the fuel rails. It functions as an electronic replacement for a traditional, mechanical fuel pressure regulator. A pressure vent valve within the fuel tank provides an added measure of fuel pump flow control module (FPCM). Desired fuel pressure is commanded by the engine control module (ECM), and transmitted to the FPCM via a GMLAN serial data message. A liquid fuel pressure sensor provides the feedback the FPCM requires for Closed Loop fuel pressure control.

Fuel Pump Flow Control Module (Gas except LU3/LMG/LY6/LC9)
Mounted to the rear frame, near the spare tire mount
Wheels/Vehicle Underbody Component Views
Component Connector End Views
Fuel Pump Relay - Secondary (Gas with LY6)
On the fuse block - underhood bracket

DTC P0191: Fuel Rail Pressure (FRP) Sensor Performance
DTC P0192: Fuel Rail Pressure (FRP) Sensor Circuit Low Voltage
DTC P0193: Fuel Rail Pressure (FRP) Sensor Circuit High Voltage
DTC P0230: Fuel Pump Relay Control Circuit
The engine control module (ECM) sends the fuel enable signal to the fuel pump control module (FPCM). The control module monitors the voltage on the fuel pump relay control circuit. If the control module detects an incorrect voltage on the fuel pump relay control circuit, a fuel pump relay control DTC sets.
The control module monitors the voltage on the fuel pump relay control circuit. If the control module detects an incorrect voltage on the fuel pump relay control circuit, a fuel pump relay control DTC sets.
DTC P0231: Fuel Pump Control Circuit Low Voltage
DTC P0232: Fuel Pump Control Circuit High Voltage
DTC P023F: Fuel Pump Control Circuit
DTC P025A: Fuel Pump Control Module Enable Circuit

Your best bet , take it to a qualified repair shop , dealer .

favorite local auto parts store

fuel gauge in tank is a common problem for GMC truck

fuel gauge have nothing to do with the cruise control ,, look if cruise module is hook up to trottle body. and with scanner read data of cruise set.resume and switch on/off function.

hope it helps

They didn't have a fuel pressure sensor in 2000.... are you referring to the fuel tank pressure sensor? That sensor measures the vacuum/pressure in the fuel tank and is related to evaporative emission control. That sensor is externally located directly on top of the fuel pump on top of the fuel tank. It has a 3-wire connector plugged into it.

have u replaced fuel filter?

the fuel pump is inside the fuel tank. some techs just lower the fuel tank down, others remove the bed. personaly dropping the tank is harder, but lifting off the bed requires about 4 strong people.

pull the bed off or drop the gas tank

SOUND LIKE FUEL PUMP WEAK OR FUEL TANK FULL OF SEDIMENT.CHECK FUEL PRESSURE.IT SHOULD BE 9 - 13 PSI FOR TBI FUEL INJECTION SYSTEM. 55 - 61 PSI FOR MULTIPORT FUEL INJECTION SYSTEM.IF FUEL PRESSURE IS LOW REPLACE FUEL FILTER FIRST.IF THAT DONT HELP.FUEL PUMP BAD.

Did you change the fuel filter? A partially clogged fuel filter will burn up a brand new pump. Otherwise I would suspect you just got a brand new bad fuel pump. Has happened to me twice, so it is possible. Some parts I pay more for to get the OEM brand. Fuel pumps, water pumps, heater core, etc. Any hard to replace part, I buy from the dealer or from a parts store that sells the OEM brand.