I have a FAST ECU with a stand alone harness in my car and I need to rewire my fuel pump relay harness. The FAST harness has a ground wire for the fuel pump relay and right now I have the OEM relay rewired a little bit to get it to work the way FAST says. The problem now is that the relay connector is worn out and I would really like to rewire the entire fuel pump with a new 40 amp relay and larger gauge wire. At the same time, I want to get rid of all the little wires attached to the relay that dont serve any purpose now like the wires that run to the oil pressure switch which is uselss now and all the other wires that are spliced into other things. My question is, do I just wire up the fuel pump relay like it is suppose to be wired and connect the FAST fuel pump - output wire to the - wire on the relay or do I have to rig this relay up like my OEM one?

 

Oil pressure part of the wiring is a redundant part of the system which works only is the FP relay fails---gives power supply to the fuel pump when oil pressure (during crankting to start the engine0 is enough to close the switch.
Wire the fuel pump with battery voltage supply and switched ignition power.
Actuate the relay with ground wire from ECM. Use ten or twelve wire to make sure of enough current for the fuel pump.

 

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All relays work pretty much the same---most are normally open and close when the windings have power to them although they can be wired so that they are normally closed and power opens them up. An example is low oil pressure relay that shuts off the ignition if you lose oil pressure.
Your oil pressure part of the relay is after the fuel pump relay and only works if the fuel pump relay doesn't ie it is hooked up on the power out side....
Hook up your relay with ignition switched power to one side of the winding.
The FAST ground wire is what will actuate the relay if you have power to the other side of the winding. (Most stock ECM do the same thing.) The power which is then switched by the relay is twelve volts from the bat or starter solenoid (still bat) to the relay and when the relay is closed it passes the twelve volts on to the fuel pump. Most stock power supply wiring to the pump is barely adequate for stock fuel pumps and it is certainly not a number 10 or 12 size wire required for a high performance pump. The last thing you want is to spend money for a good pump and then suffer voltage drop because of inadequate sized wire. You vary the speed of a DC motor by varying the voltage---lower voltage= slower speed. Higher voltage means faster speed, therefore any voltage drop in the line to your pump will slow it down. Jim