1991 NA to 1993 Turbo Wiring

[Basement Digital]

This is supplemental information to my 3SGTE swap write-up located here: MK2 NA > Turbo Write-Up

Although relevant to the aforementioned write-up, I've put this information into a separate post is because it is probably the most difficult part of the swap. Also, I am including pictures and information that came from another project that I finished many months later.

As detailed by my original post, this wiring process is essentially the only thing that prevents the 3SGTE swap from being "plug and play".


Ok, so a little review here:

There are two primary wiring looms (harnesses) relating to engine control, function, etc. The Body Harness and the Engine Harness.

The Body Harness runs from the kickpanel inside the cockpit of your MK2 to the fusebox located in the engine bay. It also runs from the fusebox thru the rear firewall to your ECU with plug A .

The Engine Harness is attached to your engine, sensors, injectors, etc. It also runs thru the rear firewall to your ECU with plugs B & C, and also connects to your starter relay.



As mentioned, both harnesses attach to your fusebox, although it's quite easy to disconnect the Engine Harness from the fusebox. The Body Harness is not. You may as well consider it permanently attached.

When you purchase a 3SGTE it will either come with the fusebox attached to your Engine Harness with a cut Body Harness stub hanging off of it, or an Engine harness that has hopefully been disconnected (as apposed to cut) from the fusebox.


If your engine came with the fusebox it's pretty easy to compare the two, determine what needs to be pillaged, and make the necessary changes.

NA fusebox bottom:


Turbo fusebox bottom:


Wires to swap comparing the two:



So what to do if you don't have a turbo fuse box to compare/pillage? Well you need to get a little creative. That's exactly what I did for another board member.
Read on if you think you can handle it, or pm me if you're interested in having me do it for you.

I started by tapping one of the wires with a suitcase connector as pictured below. You can easily run the other wire up to the top side of the fusebox for the next step, but neatly cover the connector in electrical tape after you're done splicing to prevent corrosion.



Once up top, take another suitcase connector and splice the two wires from the engine harness together as pictured. (Ignore the fuse tap wire pictured. It's unrelated)



The next step I unfortunately do not have a picture of, but it's very simple. Just add a third suitcase connector to one of the wires you've spliced together and splice it to the wire that you've added from the underside of the fusebox.

Carefully cover the connectors with electrical tape and you're done with this fusebox nonsense!

Ahhh, but not so fast! You still have plug A from your NA body harness to fix up.

ECU plugs B&C will work with the 3SGTE ECU since they came with your motor. Unfortunately Plug A will not work because the 5SFE ECU is different. Your objective will be to hack off Plug A and splice on one that will work. I took one from another vehicle on my first swap. I have since found this source for 3SGTE ECU pins and plugs brand new!! This makes the swap much cleaner.

Use the following information to identify each pin on plug A.



Pins shared between 91 NA & 93 JDM Turbo:
(Wire colors listed are from the NA body harness side)

• BATT: 12V constant. - White w/ Red
• +B: 12V keyed. - Black w/ Yellow
• +B1: 12V keyed. - Black w/ Yellow
• * FC: Fuel cut (circuit opening relay). - Green w/ Red
• ELS: Engine idle up Diode. - Black
• W: Warning light. (check engine light) - Green w/ White
• SPD: Speed sensor. - Purple w/ White
• PSCT: Power steering. - Blue w/ Yellow
• PS: Power steering. - Black
• A/C: Air conditioning. - Black w/ White

Unused NA pins:
(Tuck these cut wires away and tape over them!)

• VF: This pin is located on the engine harness plug 'B' for turbo models. - Purple w/ Yellow
• ?: Mystery pin. According to my 91 service manual this wire should not exist. I've rewired two 91 NA's to turbo now and found this wire on each car. - Pink w/ Green

Unused turbo pins:
(These are not present on the NA plug and are unessential)

• ABS: Anti-lock brake system.
• STP:
• RLY/FPR: Fuel pump relay.

Start by peeling away that electrical tape and tubing. Label each wire with some tape and a sharpie as pictured below.



Once you're sure that you've labeled each wire correctly, karate chop that sucka off!



Strip the tip of each wire.



Crimp a pin to the end of each wire and snap it into the new connector. I recommend doing each at a time since there are two different pin sizes.



Once you're done, cover the wires in electrical tape. You may notice that I've added one wire that is loose - more on that in a moment.



Put the stock tubing back on (You may need to shorten it slightly first) and tape it up for that clean stock look!



Ok; more on the red wire that was pictured above:

• STA: Starter. You must run a wire from this pin on the ECU to the the starter relay pin pictured. This is because turbo models utilize plug 'A' and NA's utilize plug 'C'. If you skip this step the car won't start!

Please note that the STA wire pictured above was from a different swap than below. In the swap above I used a red wire, below I used a green w/ silver wire. Obviously the color doesn't matter - but I figured I'd do that just to confuse you guys.



The EA1 connector always seems to be an afterthought for me. Probably because it is not critical to motor function. See below for pinout information if you are concerned about it - otherwise; ignore!



Pin - Color : Desc.
1 - ? : ?
2 - not used
3 - L-O : Engine bay fan sensor
4 - L : Engine bay fan sensor
5 - L-W : Fan warning light (to instrument cluster)
6 - not used
7 - W-B : Ground
8 - R-G : Engine hood switch (for factory alarm)
9 - not used
10 - V : Speed signal (from speedo to ECU on 91-92 car)
11 - L-B : MAP ("boost sensor") to stock boost gauge
12 - L-B : FP diagnostic (to check connector)
13 - not used
14 - not used
15 - G-W : Check Engine Light (to dash)

L = Blue
G = Green
O = Orange
W = White
B = Black
R = Red


Congrats! You've just saved $1,500 (for a clip) or $800 (for a turbo body harness).

If you want to save money but can't do this work yourself - pm me!