What is needed to complete the wiring harness conversion?

1. rb25det engine wiring harness
2. s13 ka24e or de engine wiring harness
3. rb25det lower harness
4. s13 ka24e or de lower harness
5. soldier
6. soldiering iron
7. wire cutters and stripers
8. Tape and heat shrink.

O2 and MAF sensor wiring:
You will need to identify these two plugs. The O2 sensor is a three wire gray plug, the maf sensor is a five pin plug yet only has four wires, and it’s the only plug of this kind. These two wires are pretty easy, they simply need to be made longer. These are shielded wires so you will need to make sure that they stay that way. The easiest way to do this is to use the O2 and MAF sensor wires from your stock KA engine harness. Carefully cut away the factory tape and wire loom to expose the wires on the KA harness, you can easily remove the large thick gray wires of the MAF and O2. 

Remove as much as you can. Going back to the RB harness cut the harness the same way as the KA harness, cutting all the way back to the firewall grommet. Simply cut and remove the MAF wiring and replace it with the KA MAF sensor wiring. Do not forget to swap the KA MAF plug for the RB maf plug. Pay attention to what color wires on the RB harness you connected the KA wires to, and then connect the MAF plug to the same wires. Do the same process for the O2 sensor. It really is that easy just pay attention double check for any loose or exposed wires. Always heat shrink and retape all soldier joints.

Transmission Interface:
The transmission interface, not to be confused with the lower harness which includes the transmission harness, is usually easily identified as a rectangular gray plug with a rubbery plastic shielding. Carefully remove the tape from the entire string of wires that contains the transmission interface plug. Though not all of these wires will be used, some are very important. This string of wires also contains the power steering plug, which we will be deleting as well. Once you have untapped the wires you will find a Blue/red stripped wire, 12v switched; a Blue/white stripped wire, also 12v switched; a Gray wire, the injector power wire; and a Yellow wire, the fast idle valve power wire.

Start by holding the Blue/white and the gray wire together as close to the firewall grommet as possible and cut them off together. Now strip both wires and soldier them together. Next repeat the same steps for the Blue/red and Yellow wires. Now your injectors will have power as well as the fast idle valve.

For the remaining wires in this string, start by cutting off the plugs. There are a few check connectors in there you can keep them if you want or pull them back to the ECU and remove them it’s up to you. First let’s look at the Green/orange stripped wire it’s the neutral safety switch wire. Pull this wire back to the RB dash interface and cut it off at the interface plug, leaving the portion that goes to the ECU. Next is a Yellow/blue striped wire, the tachometer wire. Do the same steps with this wire as you did with the neutral safety wire. Now you should be left with 6 wires remaining in this string of wires. A Light blue wire, a Green/red stripped wire, a Light green wire, a Green/black stripped wire, a Black wire, and a Black/yellow stripped wire.

The Black wire and the Black/yellow wire simply need to be cut a short as possible and taped up, so as not to come into contact with any other wires. These two wires are for unused check connectors, so they don’t need to be connected to any thing. Next pull the Light blue wire, the Green/red wire, the Light green wire, and the Green/black wire back to the ECU and remove them completely as they are not needed in this harness.

Wiper components removal:
Locate the string of wires designated for the wiper motor and the wire amplifier, they look the same as the plug and amplifier for the S14, but are not needed on the S13 engine harness. Start by removing the tape from this string of wires. There is one very important wire in this string, it’s the Blue/red stripped wire that you are using to power the fast idle valve. You will notice that there are two of these wires, one coming from the RB dash interface and one going out to the engine compartment. Hold these two Blue/red stripped wires together as close to the firewall grommet as possible and cut them together. Now strip and soldier these two back together, if you don’t do this your fast idle won’t have power.
Cut the remaining wires from the plugs and pull those all back to the RB dash interface. You will be removing 6 wires from the RB dash interface, a Brown wire, a Green/red stripped wire, a Green/black striped wire, a Brown/white stripped wire, a Blue/yellow stripped wire, and a Purple wire, all need to be removed from the RB dash interface. Pay attention to the Blue/red stripped wire; you will need to give this wire power when you introduce the KA power interface wires.

Introduction of the KA power interface:
Start by removing the power interface from the KA engine harness. This section is easily identified by a Gray and a Red plug that plugs in behind the underhood fuse block. Remove as much of this string of wires as possible as far back as the ECU if you can. The portion going to the main engine harness is not needed. Only a few of these wires are needed, 5 to be exact, a Thick Black/red stripped wire “switched 12v”, A Red wire “constant 12v”, a Green/orange wire “neutral safety switch”, a Black/purple wire “fuel pump relay”, and a Green/yellow wire “a/c relay”. Cut all of the remaining wires at different lengths and tape them up so as not to come into contact with any other wires, they are not needed for this swap.

Feed the KA power interface through the RB firewall grommet, leaving enough wires from the power interface reaching through the grommet to reach there original locations in the engine bay. Now to connect the five wires we left in the KA power interface to the RB harness. Let’s start with the Thick Black/red wire on the KA harness, connect this wire to 3 different wires from the RB dash interface, a Thick Black/red wire “switched 12v”, a Blue/white wire “injector power”, and a Blue/red wire “fast idle”. Next is the Red wire “ constant 12v” from the KA harness, connect this wire to 2 different wire from the RB dash interface, a Red wire “constant 12v”, and a White/black wire “constant 12v”. Next is the Green/orange wire “neutral safety” from the KA harness, Connect this wire to the Green/orange wire “neutral safety” from the RB dash interface. Next is the Black/purple wire “fuel pump relay” from the KA harness, connect this to the Black/purple wire “fuel pump relay” from the RB dash interface. Finally stretch the Green/yellow wire “a/c relay” from the KA harness to reach the wires that are going to be connected to the hybrid s13/r33 dash interface.

Creation of the new dash interface:
Let’s start by cutting the dash interface plug from the KA harness. We have 7 wires to connect here and then we are finished with the engine harness. Next by identifying the 7 wires on the S13 dash interface. First we have a Yellow/black wire “speed sensor”, next we have a Yellow/red wire “Tachometer”, then a Blue/black wire “temp.”, a Blue/green wire “a/c relay”, a Black wire “ground”, an Orange wire “start signal”, and a Red wire “check engine light”.

Now from the RB dash interface you will need to pull back 7 wires to about 6 or 7 inches past the ecu plug. These wires are a Yellow/green wire “speed sensor” to be connected to the Yellow/green wire “speed sensor” of the S13 dash plug. Next is the Yellow/blue wire “tach.” to be connected to the Yellow/red wire “tach” of the S13 dash plug. Then the Blue/black wire “temp.” will need to be stretched to connect with the Blue/black wire “temp” of the S13 dash plug. The same will need to be done with 3 Black ground wires, connect these 3 together into 1 wire and stretch them to connect with the Black wire “ground” on the S13 dash plug. Now the Gray/red wire “start signal” needs to connect to the Orange wire “start signal” on the S13 dash plug. Finally the Red/white wire “check engine light” from the RB dash plug needs to be connected to the Red wire “check engine light” on the S13 dash plug. This should complete your RB25DET/S13 wire harness conversion. Double check all connections, make sure all wires are connected as they should be to the right wires, and remove all remaining wires from the harness.

I have written this to the best of my knowledge, from research and experience. Though I cannot and will not be held accountable for any mistakes. Follow this guild to the letter and you will not have any problems. If you want a warranty send your harness to a professional. I will do your harness for you at a cost of $150 plus shipping, that’s cheaper than most places and mine comes with the same guarantee.