91 blazer 4.3 not getting fuel to motor

Hello. Your Chevy's fuel pump assembly color code wiring should be grey (power) black (ground) purple (fuel level) and orange (low fuel warning). To check, attain a 12 volt test light and probe the wires one by one as an assistant turns the switch on and off without engaging the starter. Good luck and keep me informed; if you want to.

no bypass. There is no switch (Fords only) there are several relays that are th esame, you can swap it with the horn relay. You should be able to hear the relay turn the pump on for 2 seconds when you turn the key on. Sometimes you can give the bottom of the fuel tank a rap and it will get pump going again for a short time, If that gets it going, replace the pump ASAP.

Black/white is A,........ Green is B ......and Gray is C

its more likely the sending unit resistor inside the tank. sometimes you can replace just the float resistor with another working used one but most new ones come only as the complete unit

Was the wire harness replaced from the fuel sending unit to the frame, it's a good practice to replace the wire harness when the sending unit is replaced. The wires are know to break and cause sending unit issues from weak fuel pressure to faulty gas gauges.
The other possibility would be a faulty connection to the stepper motor in the gauge it self or just a faulty stepper motor that would need to be replaced. You can do a search on Ebay for stepper motors for your fuel gauge which runs for around $15.00 which is much better then $400.00 for a new cluster if it is and bad fuel gauge stepper motor.
Thank you for using fixya and good luck.

Try changing the fuel pump or the fuel pump relay ECMB fuse controlls the pump control.

Jump in! 8mm, 10mm, 12mm, 14mm, 17mm. There is a hooking bracket on the head near the ps pump and a hooking bracket on the transmission. Loosen everything, unplug everything, drain coolant, pop axles out and lift them both out at the same time. If you're putting another motor in, try to get the same as yours according to external coil or internal coil on the distributor. 90 or 91 is easiest with your car. If not you'll be swapping your entire wiring harness. If you're putting an EX motor in an LX car (or other way around) you'll also need to change the header "o2 sensor is in a different spot", AC pump bracket and AC pump. I put a 93 EX in a 90 LX and it is fine! Extra work but runs great.

Your fuel pump relay is triggered by your oil pressure switch,try jumping across to bypass your fuel pump relay if truck runs then figure out why relay is not being triggered.

did you recently change the fuel pump? If so you needed to change the wire harness thats attached to the fuel pump, then if not, your floater need to be replaced inside your fuel tank.
How do I know? from experience.

it is located in the fuel sending unit at the top of the tank. You have to remove the tank to get to it.