HowTune

Replace The Backup Light Switch on a Subaru Impreza WRX STI 6MT

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This project will go down as one of the most annoying simple projects. The switch is such a simple, seemingly easy to replace part. However it's located in the worst location - the top of the transmission.

I highly recommend you rule out bulbs, fuses, and wiring issues before you begin disassembling the car in order to replace the switch.

Estimated total project time: 6 hours, start to finish. Having never removed the exhaust, driveshaft, or transmission before. It'll take less time if you have more experience with these cars, or for that matter, have a lift.

Oh yea, the Neutral Safety Switch

For what it's worth, the neutral safety switch in the same location. It's almost exactly the same (it has a different connector). If you're the type that likes to replace things that are hard to get to while you're there - you may want to buy that switch and replace it at the same time.

  • 10-19mm sockets and ratchet
  • open ended wrenches for the driveshaft
  • 19mm crows foot
  • lots of extensions
  • jack
  • jack stands

Prepare The Car

1

Raise the Car.

Use either on a lift or 4 jack stands.

If you're on your back under the car, get the car up as high as you safely can. I didn't have enough room to squeeze my arms between by torso and the floor of the car, which made things more difficult.

Diagnose a Broken Reverse Light Switch

This section is optional - if you'd like to verify the switch itself is broken before you go through the headache of removing it - here's what you do:

2

Disconnect the reverse switch connector.

Note the reverse switch has a black wire sleeve and a white connector. The neutral safety switch is the opposite.

3

Option 1:

Plug a new switch into the connector and manually press it in to test. (the ignition keys must be in the on position)

Options 2:

Using a multimeter set to read ohms (mine was set to 200).

Insert the probes into the prongs on the broken switch's connector.

When the car is NOT in reverse, the meter should read infinite (open). When the car is in reverse, the switch closes - which will read a very small amount of resistance.

Option 3:

Use a multimeter set to read ohms. Locate the transmission harness located under the intercooler and disconnect it. Check the ohms across pin 3 and 6. They connect to the switch so you can use the same assumptions as option 2: In reverse, ohms should be less than 1, otherwise it should read as open.

Image 8771 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT

Disconnect Pitch Mount

4

Disconnect the battery.

Image 8770 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
5

Remove the top mount intercooler to gain access to the pitch mount.

There's a detailed guide here on Howtune for Removing the TMIC.

6

Disconnect one end of the pitch mount. There's no need to completely remove it, we just need it out of the way.

I put the bolt back in the empty hole so I didn't lose it and it'll help keep the pitch mount from resting where it could prevent the engine from moving.

Remove Exhaust

7

Remove the 2 x bolts that connect the catback to the midpipe.

Image 8774 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
8

Remove the exhaust from the car. You'll have to wrestle with 4 rubber exhaust hangers. They "just" slip out of the rubber with a lot of squeezing and swearing.

Disconnect the Rear Driveshaft

9

Mark the joint between the front and rear of the driveshaft. It's probably best to assemble them in the same orientation they came apart.

10

Split the rear driveshaft in half - there are 4 bolts holding the halves together.

Due to the driveshaft's shape, I needed to use 2 wrenches to loosen the bolts. Though you may be able to use an impact with a wobble extension.

Image 8777 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
Image 8778 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
11

Disconnect the driveshaft/propshaft bearing from the car.

If you're careful, the front half of the driveshaft will just hang from the transmission.

If the driveshaft comes out of the transmission tail shaft, transmission oil will come out.

Image 8788 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT

Pitch the Engine and Transmission Down

12

Place a jack under the transmission.

We placed the jack directly under the transmission mount using a small metal plate to support the crossmember.

Image 8779 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
13

Remove the 4 rear crossmember mount bracket bolts

14

Remove the front 2 x 17mm crossmember bolts. (M12x1.25)

15

Loosen the 2 motor mount nuts that connect the motor to the engine crossmember.

Just back them off all the way and thread them back on a few turns.

16

Slowly lower the jack till you have enough room.

I'd advise you lower it an inch or two at a time and check to make sure nothing under the hood is being stretched or crushed.

Replace the Backup Light Switch

17

Locate the reverse light switch.

It's conveniently located on the top of the transmission. To get an idea of how inconvenient this really is: Imagine the floor and transmission tunnel of the car around the picture below.

The floor is basically even with the bottom and the tunnel is only a few cm or 2 larger then the transmission.

There's no space. You can't even see the switches without lowering the transmission!

Image 8790 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
18

Disconnect the connector

Image 8783 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT
19

Using a 19mm crows foot, wobble socket, and a handful of extensions - remove the switch.

I saw everyone complain about how tight this switch is - it turns out they were right. It's a little dumbfounding why these switches are so tightly installed, but it'll take more effort than you expect to remove them.

When finally put enough force on them to break them loose, my extensions, wobble sockets, and crows foot shot everywhere.

20

Carefully thread the new switch in.

Take your time, go slow, and it'll work. I'm going to brag a bit here - I manage to get it to thread the first time in less than 180deg of rotation.

21

Connect the new switch.

22

Test the switch.

Connect the battery, ignition on (not started) and move that gear selector into Revers.

It's ok to shout with excitement when it works. We took a break at this point.

Image 8769 from Replace the Backup Light Switch on a Subaru Impreza WRX STI 6MT

Reassemble

23

Lift the transmission to re-align the crossmember mounting points.

24

Install the 2 front transmission crossmember bolts. Tighten to 75 ft-lb / 103 Nm.

Note: there's an error in the maintenance manual listing these as 103 ft-lb / 140 Nm. That torque is beyond the rating for the fasteners.

25

Install 4 rear transmission crossmember bolts. Tighten to 51.6 ft-lb / 70 Nm

26

Tighten engine mount nuts. Tighten to 62.7 ft-lb / 85 Nm

27

Reassemble the rear drive shaft.

Tighten the 4 bolts holding the 2 halves together to 28.3 ft-lb / 38 Nm

28

Install the exhaust

29

Install the engine pitch stop

  • Pitch stop body mount: 42.8 ft-lb / 58 Nm
  • Pitch stop transmission mount: 36.9 ft-lb / 50 Nm
30

Install the top mount intercooler

31

Connect the battery and you're don

  • Rear driveshaft / propeller shaft bolt torque: 28.3 ft-lb / 38 Nm
  • Rear driveshaft center bearing to body: 38.3 ft-lb / 52 Nm
  • Pitch stop body mount: 42.8 ft-lb / 58 Nm
  • Pitch stop transmission mount: 36.9 ft-lb / 50 Nm
  • Transmission crossmember (rear to body): 51.6 ft-lb / 70 Nm (M10x1.25)
  • Transmission crossmember (front to body): 75 ft-lb / 103 Nm (manual error shows 103 ft-lb) (M12x1.25)
  • Engine mounts to crossmember: 62.7 ft-lb / 85 Nm
  • Backup light switch: 23.6 ft-lb / 32 Nm

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