The RB20DET is a subset of the RB Nissan inline turbocharged engines, and while it’s not as popular as the RB25DET or 26, it’s still a plenty nifty engine. Able to rev to 8000 RPM and even more with some cylinder head work, the RB20 makes up in fun what it lacks in displacement.
Like the 2.5 liter version of the 2JZ, the RB20 is significantly cheaper and in some cases more cost efficient than a SR20DET swap would cost. A long way in lowering the cost of your engine swap will involve you knowing how to wire a RB20DET into a S13.
Today we’ll be showing you how to wire a RB20DET into a S13 using a stock RB harness and a stock S13 harness. If you haven’t already look up our How To Guide on swapping a RB25 for a basic primer on how to swap an RB engine into your USDM Nissan. Our How to guide covers such topics as driveshaft length, wiring into a S13, a S14, motor mount review, and much much more.
The test vehicle we are wiring this Rb20DET into is a SOHC 1989 Nissan 240SX. and we’ll be assuming you’ve already removed your stock KA24DE engine. If you need a how to on removing your stock engine, check here.
The first plug we’ll be looking at is the S13 Brown power plug located in the engine bay, near your passenger side headlight.
The first wire you’ll be taking a look at is the Fuel Pump input, which is a black wire with a pink stripe. This wire is a crucial component of your RB20DET swap, so make sure to tag this so you can come back to it.
The next wire on the brown S13 plug is the neutral switch, depending on the model of your S13. The IACV sensor power wire is the black wire with yellow stripe, and the two brown wires are the 02 sensors for your KA24DE. Finally the red wire with black stripe is the ECU relay, also another big part of your RB20DET S13 swap.
With this plug cataloged, let’s take a look at the gray oval plug that’s next to your brown plug in your engine bay.
Coming off the passenger side fuse box, the gray plug has many of the important wires needed for your RB20 S13 swap. You’ll also notice that some of the wires in this gray plug are larger than the others, signifying that it’s a main power wire from the chassis. The main ignition power is the thicker gauge Black wire with Red stripe, and the ECU Backup power is directly next to it as a solid RED wire.
The main ECU power is the black wire with white stripe, and the solid black wire is your low reference or chassis ground. Unless you are also swapping over JDM creature comforts in your 240SX, the remaining Air Conditioning wires are not needed. Those are blue with green stripe and green with yellow stripe.
The next S13 plug we’re looking at in our How To Wire a RB20DET into a S13 article is the dash plug. This brown plug is located under the dash on the passenger side and you’ve got to tee several wires into this connector for your stock S13 tach and speedo to work. If you are looking for a How To on installing Dakota Digital translators, check our guide here.
The wires that you’ll need to tee into your RB20DET ECU harness for the dash instruments are all located on this brown dash plug. The tachometer is the Yellow wire with red stripe shown above, between the speedometer which is yellow wire with green stripe and the water temp sensor, which is blue wire with black stripe.
The other wires you will need are the orange for ignition start, as well as the black for low reference ground signal. The blue wire with green stripe is AC signal and the solid RED wire is your check engine light illuminator. Use this wire to light off your own DIY Knock Sensor LED modification, if you aren’t using it for the RB20 MIL.
And finally the steering column where most of your power wires and switched powers can be teed from. You may not need to access the steering column because there should be enough sensor power to tee from, and enough grounds and switched powers for your RB20, but just in case.
There’s not much room around your ignition switch, so we won’t bother listing the colors for you. Remember that the constant 12v power is the white wire with red stripe, and that your main switched power should be the ACC position wire, shown above.
With the stock S13 wiring out of the way, now it’s time to turn to your RB20 6 wire plug, this plug is the largest gray plug on your engine harness.
This RB20 6 wire plug is a big part of your RB20 swap, and it’s basically the JDM version of the engine plug you have in your S13 currently. Like your USDM plug, several wires on this plug are larger gauge than the others.
The primary ignition power is the red wire with black stripe, this wire is larger gauge than the others, like the ignition relay which is white wire with purple stripe.
The next wire on this harness is the ECU memory wire, which is the white wire with black stripe. And lastly the neutral switch is the green wire with orange stripe to finish off the RB20 six wire plug.
RB20DET Dash wiring
And lastly the RB20DET comes with a dash harness that’s similar to the USDM version, but has a large lever to lock it in place. There’s several wires here you will need, as this is not only the dash plug but where most of your sensors lead to from the engine.
We’ll start with the black wire with pink stripe, this is the fuel pump wire for your RB20DET. This connects to the same colored wire on your USDM dash harness plug located under your glovebox. Remember to always solder your connections.
The next wire on our how to wire a RB20DET into a S13, is the tachometer signal which is the yellow wire with red stripe. This wire connects to your USDM S13 dash harness and connects to the yellow wire with a red stripe, if you need a How To Install Dakota translators, look here.
The Ignition signal is the black wire with yellow stripe, connect this wire to the S13 orange wire on your dash connector. The vehicle speed sensor (VSS) is the yellow wire with green stripe and this wire connects to the yellow wire with green stripe on the S13 dash harness.
The last wire on this harness you’re going to need is the Orange wire with black stripe, this can also be a PINK wire with black stripe. This is the MIL light for your RB20DET, and it goes to your USDM S13 dash connector if you are not opting to eliminate the check engine light. Connect this to the SOLID RED wire on your USDM S13.
The remaining wires on this RB dash plug are the teal wire with red stripe, which is the AC switch and the solid light green or teal wire which is the AC relay.
RB20 6 wire plug
Much like the dash plug, this gray 6 wire plug looks a lot like a USDM ignition switch plug and will connect to the brown / gray combination plug on the USDM vehicle. Let’s start with the Main ignition power wire, which is the larger gauge wires on both the RB20 and the S13 plugs.
Connect the black wire with red stripe wire on your RB20DET harness to the black wire with red stripe on the S13 gray body connector. Make sure this wire solder connection is clean and without excess solder.
Next is the white wire with black stripe, this is the constant power or ECU memory, this must be run to the red wire on the S13 plug.
The Neutral switch is next and like many of these wires, the colors match for the S13 in green wire with orange stripe. Connect this to restore the neutral switch operation.
Lastly is the ignition relay, or the wire that leads to the blue relay under your dash. This wire is a white wire with purple stripe on the RB20 plug, connect this wire to the white wire on your S13 harness.
You have now wired in your RB20DET ECU, and there’s just a few wires left until you can fire up your newly swapped S13. Many people have questions about the lower power harness in this swap, and think they have to hardwire this unit inline with the RB20 ECU harness. In fact however, you can just re-use your factory S13 lower harness as everything still plugs in and works outside of the oil pressure sensor.
The oil pressure sensor for any RB swap will be a little tricky, you must either move to a JDM version of this temp sensor and use a translator, or go with an aftermarket gauge and stick with the S13 unit.
The last step in our How To wire a RB20DET into a S13 article is extending the MAF and 02 wires so that they can reach your components. Because this engine and ECU harness were originally JDM, the lengths in which the original wiring can reach are limited. Make sure to use shielded wire for this step, because you want the cleanest signal possible from these two sensors.
That does it for our how to wire a RB20DET into a S13 Guide, please leave any questions or comments for us below! Thanks for reading!
Need more RB DIY articles?
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How To Service RB25 Valvetrain
How To Change your RB25 Headgasket