AWD & 5MT Electrical info and notes
Electrical Tech. Notes
The electrical portion of this swap can present some challenges/issues. If addressed completely, the car will retain all factory safety features, and perform like it came from the factory with a manual transmission.
Return to Swap Intro
Electrical connector/relay info
Electrical unit locations
ECU MT/AT Identifier
Starter interlock relay
Reverse lights
Neutral switch
Shift lock (key interlock) system
Cruise control
TCU
This first section is more or less a quick overview of the electrical connectors and relays you'll need to be familiar
with for the electrical modifications. There are several different type of relays used in the car's electrical system.
The following scan shows the different types.
Relay Information
The following is a list of the relevant electrical connectors and what system they're related to.
ECU Connectors
B48 - AT/MT identification
B58 - Neutral switch
Ignition System
B63 - Ignition switch
Starting System
B15 - (AT) Inhibitor switch
B45 - Clutch switch
B92 - Starter interlock relay
Engine Electrical
B15 - (MT) Neutral switch
B15 - (AT) Inhibitor switch
B36 - Combination meter
Back-up Light
B15 - (MT) Back-up light switch
B15 - (AT) Inhibitor switch
AT Shift Lock System
B69 - AT shift lock control unit
Cruise Control
B88 - (MT) Clutch switch
B83 - (MT) Clutch relay
B83 - (AT) Inhibitor relay
The list below contains information regarding the electrical unit locations for the various relays, control units,
switches, sensors, diodes, etc. that are found on the car.
Electrical Unit Location Index
Index
Relay
Engine Room
Instrument Panel
Compartment / Luggage Room
Control Unit
Instrument Panel
Compartment - Luggage Room - Trunk Room
Switch
Engine Room
Instrument Panel
Sensor, Valve, Solenoid, Etc
Engine Room
Engine
Compartment
Diode, Condenser
Instrument Panel
Trunk Room / Luggage Room
Fuse and Fusible Link
Engine Room / Instrument Panel
Select Monitor Connector and Check Connector
Instrument Panel
Electrical Wiring Harness and Ground Point
Sedan / Wagon
Subaru does use different ECU's between the MT & AT equipped cars, however there is a MT/AT identifier pin on the ECU's.
This pin tells the ECU whether the car has a manual or automatic transmission. The pin can be found at pin 20 on the
ECU's B48 connector. The factory manuals state that for AT's the MT/AT pin should read 0v, and the MT's should read 5v.
The ECU has a reference voltage that it sends to this pin. If the pin is grounded the voltage will read 0v. That pin is
grounded on the automatics. All you have to do is snip the wire going to the MT/AT pin, and the ECU now knows the car
has a manual transmission.
Note: I swapped a 1992 ECU in my car to match the 1992 injectors I swapped in. When I put in the new ECU I
found that the MT/AT identifier pin was wired backwards to what the factory manuals stated, and to how my 1990 ECU was wired.
So I re-attached the wire that went to the MT/AT identifier pin, and the 1992 ECU was now setup for the manual transmission.
Here are the ECU I/O pages from the factory manuals that I used.
ECU I/O Page 1
ECU I/O Page 2
ECU I/O Page 3
The starter interlock relay is the safety device that keeps you from starting the car unless the clutch is fully depressed.
In the automatic cars, the inhibitor switch, which is located in the transmission, keeps the car from starting unless the
gear selector is in park or neutral. In the automatics pins 11 & 12 on the B15 connector are the pins that are connected
to the IG-1 ignition circuit, and starter relay.
When you swap in a manual transmission you have a couple choices. You can run a relay to pins 11 and 12 of B15 connector,
and then run the clutch switch to the trigger lead of the relay. Since I had access to a donor car, what I did was snag
the stock starter interlock relay and harness, as well as both sides of the connectors for the ignition circuit. I then
made a plug-in harness that put the starter interlock relay in between the ignition circuit connectors. I then hooked the
clutch switch up to the trigger lead of the interlock relay. Finally, I had to jumper together pins 11 and 12 of the B15
connector. I could have easily put the relay in the engine compartment and routed the clutch switch wire into the cabin,
but chose to go for the "plug and play" method.
Here is a picture of the custom "plug and play" harness.
I used the following pages from the factory manuals to decipher and wire up my harness.
Power Supply Routing Page 1
Power Supply Routing Page 2
Starting System
Inhibitor Switch Table
The reverse lights were for the most part pretty straight forward. The automatic cars have a 12v supply going to the
inhibitor switch in the transmission. When the gear selector is moved to the reverse position, the 12v signal is sent
through the inhibitor switch to the reverse lights. The corresponding pins for the automatics are pins 9 and 10 on the B15
connector. The manual transmission is setup similarly, except it uses a reverse switch inside the transmission. So I just
wired pins 9 and 10 from the automatic's harness to pins 2 and 4 of the MT's B15 connector.
I again wanted to keep things as "plug and play" as possible, so I cut the B15 connector and harness from the automatic
transmission, as well as the B15 connector from the manual transmission donor car, and spliced the corresponding pins
together to make a custom harness.
Here are pictures of the harness.
Here are the factory manual scans used.
Back-up Light
Inhibitor Switch Table
The neutral switch's operation is pretty simple. Tell the ECU & TCU (if automatic) that the transmission is not in gear.
However, the wiring is different between the two transmissions. On the manual transmissions, one lead going into the
neutral switch is grounded. The other end goes to pin 10 of B58. The ECU supplies a voltage to the circuit. When the
transmission is in neutral the neutral switch is open, so the voltage at pin 10 would be 8v or higher. When the transmission
is put in gear, the neutral switch closes and the voltage reading would be 0v.
The automatic's wiring is actually backwards. The automatic cars have the gear selector indicator on the dash. The neutral
circuit goes like this. Power is supplied to the combination meter. It's then routed through the bulb that displays the "N"
on the dash, and ties into the wiring going to pin 1 of the B15 connector. Pin 1 of the B15 connector is also tied to the
ECU & TCU. Pin 4 of the B15 connector is connected to ground. When the inhibitor switch is moved to the neutral position,
the circuit is completed to ground. When this happens, current will flow through the bulb in the combination meter, and
the bulb will light up. The ECU again supplies a voltage at the neutral switch pin. When the circuit is grounded, the
voltage reading at pin 10 of the B58 connector will be 0v.
The question is, "How do we get the manual transmission neutral switch to work properly?" For the most part, you can just
swap the appropriate leads on the transmission connectors. The only issue with that is the back-feeding of power through
the "N" bulb in the combination meter. So what I did was snip the wire at pin 18 of the B36 connector that came from the
combination meter. This eliminated any back-feeding of power into the neutral switch circuit and caused it to function
properly for the manual transmission setup. I connected pins 1 and 4 of the B15 AT connector to pins 1 and 3 of the B15 MT
connector. I again used the two wiring harnesses I cut off the donor car and old transmission, and wired up a "plug and
play" harness.
The blue B36 connector is located behind the lower kick panel under the dash on the driver's side. It's actually part of a
three connector plastic piece that is bolted to the car via the lower nut that holds on the ECU.
Here are some pictures of the B36 connector.
Here are pictures of the harness.
Here are the factory manual scans used.
Note: On the second page of the engine electrical scan they show that the cruise clutch switch ties into
the parking switch circuit. From what I can tell this is a misprint.
ECU I/O Page 1
ECU I/O Page 2
ECU I/O Page 3
Engine Electrical Page 1
Engine Electrical Page 2
Engine Electrical Page 3
Engine Electrical Page 4
AT Control Page 1
AT Control Page 2
Inhibitor Switch Table
The shift lock system is used on the automatics to keep you from moving the gear selector out of park unless your foot is
on the brake. It is also tied to the key interlock system, which doesn't allow you to remove the key unless the gear
selector is in park. Since we don't have an automatic any more, and we don't need the key interlock system, we can simply
remove the controller. This will eliminate the issues of not being able to remove the key if you left the controller in
place. The controller is found up under the dash.
Here are some pictures of the shift lock controller.
The following are some scans explaining the shift lock system's operation.
Shift Lock System Page 1
Shift Lock System Page 2
Key Interlock System
AT Shift Lock System
Keeping the cruise control was important to me. The cruise control computers are different between the MT & AT
equipped cars. There is one main difference between the computers. The two computers use two different types of
relays. The MT equipped car uses a normally open relay, while the AT equipped car uses a normally closed relay.
Because of this the computer is going to expect different signals to determine if the car is in neutral for the AT's,
and whether the clutch is not depressed for the MT's. The only other difference I have possibly noticed is how
quickly the computer adjusts throttle to keep the set speed. I believe it is slower for the MT equipped cars. The
cruise computer in the AT cars would signal the TCU to down shift if speed could not be maintained. A good example of this
would be going up a hill while still leaving the cruise engaged. It was actually a little annoying at times to have the
RPM's jump up dramatically because the cruise wanted to keep that set speed.
I ended up swapping out the cruise computer from the donor car, and I also swapped the cruise inhibitor relay for the
cruise clutch relay. I then rewired the relay. I took pin 1 of the AT's B83 connector and spliced it into pin 2
of the MT's B83 connector. Next I took pin 3 of the AT's B83 connector and spliced it into pin 3 of the MT's B83
connector. Lastly, I took pin 4 of the AT's B83 connector and spliced it into pin 4 of the MT's B83 connector.
For pin 1 of the MT's B83 connector I ran a wire over to the cruise clutch switch and hooked it up to one of the pins
on the B88 connector. I then connected the other pin of the B88 connector to ground.
After looking back at the cruise setup I could have probably just left the AT cruise computer in there, along with
the inhibitor relay. If I did that instead, I would have snipped pin 2 of the AT's B83 connector and spliced it
into the wire I ran over to the cruise clutch switch. The only unknown with this setup is, "Would the AT cruise
computer be looking for the TCU, and try to shift gears?"
Here are some pictures of the cruise computer.
Finally, here's the factory pages for the cruise control setup.
Cruise Control Diagnostics
Cruise Control Wiring Diagram Page 1
Cruise Control Wiring Diagram Page 2
The TCU controls the automatic transmission's functions. Since we no longer have the automatic transmission, we'll want
to remove the TCU so it doesn't get confused and send error signals to the warning lamps and ECU. The TCU is located
just to the left of the steering column.
Here are some pictures of the TCU
For posterity's sake and to be complete, here are the TCU I/O pages from the factory manuals.
TCU I/O Page 1
TCU I/O Page 2