I have a 1993 Mazda RX-7 FD twin turbo, and I'm having issues with the fuel pump. The pump stopped working, so I replaced it with a new one, but it still doesn't activate when I turn the key to "ON." The engine cranks but won't start. I checked the fuel pump fuse (20A), and it has power. I also tested the fuel pump relay, and only one of the four pins has voltage when the key is in the "ON" position. Additionally, I tested the fuel pump connector with a test light, and obviously, it has no voltage on any of its terminals. I haven't changed the relay yet, but before doing so, I want to rule out a wiring issue between the relay and the pump or a lack of signal from the ECU. If anyone has had this issue on an FD or knows what else to check, l'd really appreciate any help.

 

Do you know how to read a wiring diagram? It sounds like it could be the fuel pump relay or circuit opening relay. The fuel pump relay is in the front relay box by the intercooler and the circuit opening relay is in the relay box on the left strut tower.

First, a shortcut to verify the relays are getting 12v coil power is to ground the Blue/black wire at the diagnostic connector (page z-112 in the wiring diagrams for a '93), it's labeled "F/P" on the connector label. Ground the terminal with the key on, you should hear the fuel pump run.
If the fuel pump runs you have an issue with the ecu not switching the ground to the circuit opening relay or with the output wiring to the circuit opening relay. If it does not switch on do the following:

Check the 15A "engine" fuse in the interior fuse box, if it checks out then check for 12v on the black/light green wire at box the circuit opening relay and fuel pump relay with the ignition "on".
If that checks out, check for 12V on the blue wire at the circuit opening relay.
If that checks out put the circuit opening relay back in and check for 12V on the blue/red wire at the fuel pump relay. If that checks out try put a jumper between the load terminals of the fuel pump relay (blue/red and white/red) and throw the relay in the trash, 12AWG or larger jumper. If you have 12V on white/red and the fuel pump is not running then you have a wiring issue to/at the pump(ground or power), you can check the white/red wire at the fuel pump bulkhead as well.

Manuals - https://www.rotaryheads.com/PDF/3rd_gen/
Page z-28 in the wiring diagrams for a '93

Good luck, this can seem like overwhelming troubleshooting at first but it really isn't.

 

With the stock ECU the pump only runs in two conditions. the first is when you have the key in the "Start" position, second is when the ECU sees an RPM signal with the key on.
pump does not run if you just turn the key to the on position.

there is also a test connector, if you jump the FP and GND terminals in the diagnostic box, and turn the key on the pump should run