Contributed by Fiznat
The following article details the procedure for installing a DSM injector resistor box into the S13 240sx chassis.These resistors must be installed whenever the stock high-impedence injectors are swapped out for (often larger) low-impedence models.
Each injector has 2 wires on it, a red (power) wire and a different color (ground) wire.(The colors are different so that you can look in the manual and find out which gound goes to which cylinder.Mixing these up will cause you huge problems.)
If you look on the wiring diagram in the FSM, you will see that a short distance from the injectors, each of the power wires for the individual injectors combine into one single power wire which goes directly to the ECU.It is easiest to install the resistor box if you find this spot first.
Note again this is the factory wiring where the 1 wire splits into 4 for each of the injectors.This spot is right near the information plate on the firewall of the engine bay. You can see that I cut the power wire a few inches back from the point where it splits.This is where I will install the injector resistor box.
The DSM box has 5 wires on it.4 black wires which go to the individual injectors, and one white wire which is the power source.Attach the black wires to the 4 red wires after the split in the factory wiring, as shown, and the white wire to the ECU SIDE of the factory red wire (to the left as you are looking at the engine) Notice how the resistor box now takes power from the ECU, and sends out 4 power wires to the injectors.
It does not matter which of the black wires goes to which of the 4 red wires… all 4 supply a constant 12 volts to the injectors, so it does not matter if you mix them up at all.(Note the same is NOT true for the colored ground wires, which need to remain in a particular order.You should not mess with the ground wires at all during this install!)
Last step is to mount your injector resistor box and tape everything up nicely.It helps to use wire loom as well to make everything look uniform.