RDR 3000GT/Stealth Fuel Pump Rewiring Details

Part I: Stepping Up Input Voltage (underhood)

1. Normally, the stock fuel pump relay gets its power(pin #5) from the output of the MFI relay (pin #1). The first step is to disconnect pin #5 of the fuel pump relay from the MFI relay. This is where you cut the wire loop at the stock harness.
2. Now, the fuel pump relay power input (pin #5) needs to be connected to some power source so that the fuel pump can have power. Part of the point of this modification is to boost the voltage at the fuel pump, which is why the we change this input connection (pin #5) of the fuel pump relay from the MFI relay output (12.5V) to the battery's positive terminal (13.5V).
3. Connecting the fuel pump relay input directly to the battery would result in the fuel pump always being on, which is not good :-) Thus, we need a relay to ensure that the fuel pump relay input is only "on" when the MFI relay is on. That's where the extra relay comes in.
4. The coil input of the extra relay (pin #85) is connected to the output of the MFI relay (same as pin #3 of the fuel pump relay harness). That way, the new relay is only "on" when the MFI relay is on.
5. As mentioned before, the power input of the new relay is connected to the positive terminal of the battery. This connection must be fused to be safe.
6. The output of the new relay is connected to pin #5 of the fuel pump relay, which is the stock relay's input.
7. Using this circuit configuration, everything downstream of the stock fuel pump relay remains stock. This ensures that the ECU can still reduce the voltage at the fuel pump when it needs to do so (by switching the stock fuel pump relay so that the resistor is not bypasse).

Part II: Reducing Voltage Losses [optional]

1. At this point, the largest loss of voltage due to resistance in the circuit is the long (B)lack wire with a (L)ight blue stripe that runs from the output of the stock fuel pump relay (pin #2) to the input of the fuel pump (pin #3) in the trunk. This is a 14ga wire that runs the length of the car and, at maximum [stock] fuel pump current, results in about a 1.0V loss between the engine bay and the fuel pump.
2. To reduce this voltage loss, you can either replace the stock wire with a thicker one or splice a new wire in parallel with the stock wire so that both wires are used to carry current to the fuel pump. I found it easier to just run an additional wire in parallel with the stock wire.
3. As far as exactly where to connect this additional wire, the optimal solution would be connecting the new wire to pin #2 of the fuel pump relay and pin #3 of the fuel pump harness. Another, IMHO more convenient, way is to connect the new wire at the point shown in the diagram above.

Summary

• The RDR Fuel Pump Rewire modification raises the input voltage to the fuel pump at full throttle from an observed 11.2V up to a much nicer 13.5V and retains the stock functionality of reducing the fuel pump voltage under low/light loads.
• This modification requires cutting only one stock wire (3 total if the optional part is done) and uses only one relay and some wires/connectors.
• With this rewired circuit, you will not see an appreciable loss of voltage at the fuel pump during high-load conditions.
• In my experience, this modification reduced the peak loss of fuel pressure at high loads by more than 50% and reduced the frequency of loss of fuel pressure by more than 80%. I still do observe a slight (3-5psi) loss of fuel pressure under some conditions and am investigating the cause of that loss. However a 3-5psi loss is MUCH better than the 15psi loss I was seeing frequently before the rewire.