Hey,
currently building a track car FD3S. And due to regulations i have to use the fuel relay prime feature of the ECU. However, whenever i measure the voltage of the pin where the priming signal is supposed to come from i end up with a whooping 0 Volts, ive measured at the fuel relay itself, right after the ECU and also at the original fuel pump location. There is no engine hooked up at all, so the engine harness is barely connected. could this be the cause? alternatively does anybody know of a fuel relay which does the priming instead of the ECU?

 

I can't help you with your question directly. When it comes to things electrical I can get in over my head plugging in a lamp. But if you haven't already, a free download of the electrical manual is available here:
Mazda RX-7 Reference Materials (scroll down to 93 Electrical manual)
And if you're able to read a schematic the answer should be there.