Adding a 1G TCU to your 1G MT Harness

There are a couple ways to add a TCU to your M/T harness car.  The easiest of course is just swapping harnesses, but even that can get tricky due to some wiring differences.  When doing MT to AT conversion I prefer to just add the AT wiring to the existing harness.  There's 2 ways to do this:

Method 1: Take a AT harness and seperate the TCU wiring from the engine harness, so that it can be wired into your existing harness

Method 2:  Obtain the connectors off a AT car and build a harness

For both methods, take note that AT wiring changed over the years, and you need to have the connectors for your year trans.  1G NT 2.0L AT wiring can be used for a turbo car with minor changes. (Have verified this with 3 plug style - have not looked into  it with 1G 2 plug style yet, but I assume it is similar)

For Method 1, you already have the transmission side connectors wired into your TCU connectors for you.  For Method 2, you'll want to start out by matching up the wire colors between the TCU plugs and the transmission plugs.  Start cutting sections of wire to connect the two sides.  Make sure you use the proper gauge for each wire.  I usually make my harnesses approx. 3.5 feet.  Once you've connected all the wire colors from each side, there will be some wires left over on the TCU plugs.  Along with the power wire that you will need to do some things with.  Here is a chart that shows how these wires interconnect, followed by descriptions of what to do with each.

Wire Color (based on 3 plug connector) Function 1G ECU 3 Plug 1G 2 Plug 1G
Black w/ white stripe + red dash ? n/a 103 n/a
Blue w/ black stripe + red dash +12v Power 102 104 12
Black w/ red dash Ground Ground 105 13
Blue w/ black stripe + red dash +12v Power 107 109 25
Black w/ red dash Ground Ground 110 26
Yellow w/ white stripe + red dash Power Mode Signal n/a 64 38
White w/ red dash Tach Signal 109 (91-94) / 21 (90) 63 46
Black w/ red dash Ground Ground 62 45
Red w/ white stripe Overdrive Switch input n/a 57 37
Black w/ red dash Ground Ground 1 n/a
Brown Accelerator Switch n/a 3 20
Yellow w/ red stripe + brown dash Diag. Output terminal n/a 5 9
Green w/ yellow stripe + red dash AC control relay n/a 6 8
Yellow w/ green stripe + red dash Diag. control terminal n/a 8 11
Red w/ black stripe + black dash Backup Power source 103 10 39
Green w/ white stripe + red dash Throttle Position Sensor 19 16 21
Yellow w/ white stripe + red dash Vehicle Speed Sensor 18 18 40

3 Plug TCU diagram:

2 Plug TCU diagram:

Ground - Connect all grounds to ground

+12v Power - Tie these together and they will tap into a +12v ignition switched power off of the ECU, the same wires which power the ECU.  One wire will split off this same power source to a pin on the 10 pin rotary switch connector.

3 Plug TCU type rotary switch - Pin 4 needs to be given +12v power from the same source as the TCU; pins 8 and 9 are not going to be used.

Power mode signal - wire this up either to an OEM switch or to any switch of your choice.  +12v at this pin will put the TCU in power mode

Tach signal - 91 to 94 will tie into OEM tach signal.  Since 91-94 signal is inverted on a 1990, you will have to tap into the CAS wire on a 1990 harness

Overdrive switch input - This works the same as the power switch.  +12v at this pin enters overdrive mode.  Wire it to OEM or your choice of switch

Accelerator Switch - MT cars do not have this.  However, there is a switch that does the same thing.  The idle switch on the throttle body has the same logic.  For an EMS car that does not use the idle switch, you can simply cut the OEM wire and use the idle switch for this.  For an OEM ECU car, you will need to tap into this wire.  This wire is not required if you don't want to bother with it.

Diag. Output terminal - works like the ECU diag wiring; used for TCU diagnostic - not required, but can be wired up if you want diag stuff

AC control relay - never bothered to look into how this works since most people don't  run AC.  It receives some sort of signal when AC is in use.  Doesn't seem important even if you have AC.  No need to deal with this.

Diag. control terminal - used for TCU diagnostic - not required, but can be wired up if you want diag stuff

Backup power source - this wires into the same backup power source that your ECU uses.

Throttle position sensor - this ties into OEM TPS wire

Vehicle Speed Sensor - ties into OEM VSS wiring

Backup lights - Coming off of the rotary switch plug, there are two red wires, one with blue stripe + black dash, the other plain red + black dash.  These are for the backup lights.  Wire these two wires into the two wires that used to connect to the backup light switch on your manual transmission.

Pins 10 and 11 are backup lights if you have this connector.

When using a set of plugs from an early (3 plug type) 2.0 NT in your early (3 plug TCU) Turbo car, you will need to move a wire in the TCU plug and obtain a 3 pin triangle plug.  The NT harness has a 2 pin connector for the temperature senders where the early (3 plug) turbo models use a 3 pin connector with 2 temperature senders.  The NT plug has a extra wire for lockup that the turbo cars do not have.  You can remove this pin and move it to fill in the missing pin that is needed for the temperature sender.  3 plug pin 101 is the one not used, you can move it to pin (14 or 15, I can't remember which one is the missing one).  Match up the wire colors to properly add the 3 pin triangle plug such that it matches up properly to the wiring on the transmission side.