85 rx7 what does the fuel pump relay do exactly. Please spell it out in laymans term. Where can i get one and how much do they cost

 

I take it by this few post that you did not have power to the Blue w/ White stripe wire at the fuel pump??

Your fuel pump relay is actually refered to as a fuel pump cut relay.
There are two separate circuits in a relay, hence the four wires. There is a switch side and a coil side. The coil side is simply a very long wire wound into a coil that produces a magnetic field when power and ground are applied to either end of this wire. When this occurs the switch side of the relay is either opened or closed by this magnetic field .When switch is closed then power is allowed to flow thru the relay and on to the device it is controlling This is called a normally open relay or NO as the contacts are open when relay is not plugged in.This is the most common type of relay.

The type of relay in your RX-7 is called a normally closed or NC relay as the contacts are closed when relay is not plugged in. Power is supplied thru the relay and onto the fuel pump anytime the ignition switch is turned to 'on' or 'start' positions. The only time power would not be allowed thru the relay and ontothe fuel pump would be if the Emission Control Unit or ECU broke the ground circuit of the coil, eliminating the magnetic field and allowing the relay to open the contacts.
Hope this is all making sense. Not a very good teacher. There is probably a much better explanation at this link.
http://electronics.howstuffworks.com/relay1.htm

If you have located the relay under the dash then you should have voltage (test light should light) at each of the four wires when relay is plugged in and key is 'on'.
If no voltge is indicated only at the Black w/Yellow stripe wire,then ECU is grounding the coil and commanding the relay and fuel pump to be off or wire is shorted to ground somewhere.
If no voltage is indicated only at the Blue w/ White stripe wire then relaycontacts are bad.
In no voltageis indicated at any of the wires (again, key on so dash lights are illuminated) then probably have a blown fuse.

You may be able to find a generic relay from parts store as long as it is a NC or normally closed relay. Relayis also still available thru Mazda dealer (only 17 left in US and Canada warehouses).
The part number is FA55-67-740. Dealer retail is $47.05 and available fromwww.onlinemazdaparts.com for about $10 less.