How to keep your shock sensor feature on your OEM Security Alarm w/ Turbo Timer - Subaru WRX Forum
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post #1 of 7 Old 09-15-2006, 07:49 PM Thread Starter
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How to keep your shock sensor feature on your OEM Security Alarm w/ Turbo Timer

If you're reading this how-to, then you probably know that most people that have installed a turbo timer on their WRX and have the OEM Subaru Security System installed, are forced to cut the wire that goes to the shock sensor. The reason is because the vibrations from the idling exhaust can be enough to set the alarm off while it's turbo timing.

This mod takes advantage of the fact when any door or when the trunk is open and you lock your car, it will beep 3-5 times depending on your model year. After the door is shut, the car beeps once confirming that the alarm has been armed. This mod taps into the trunk sensor to "trick" the vehicle into thinking it's open while it is turbo timing, and "shuts" the imaginary door when the ignition is off. I use a normally open (NO) relay to accomplish this.

Here is a video demonstration of it fuctioning.

Some of the documentation from the repair manual I need to confirm this would work
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This tutorial will also assume a few things. I will assume:

1) the turbo timer has already been installed on the car
you can find the tutorial here (note, you must be logged in to view the photos) Do not perform any modifications that "allow your car to work with the security alarm." Especially, do not perform the one that cuts the gray wire and splices into the ACC+. This will eliminate the shock sensor feature.

2) you have preformed the modification to allow you to lock your car with the keyless remote while it's turbo timing (it will talk about cutting a dark green wire w/ a black stripe.

3) you have a basic understanding of electricity... DO NOT EVER EVER EVER let a live/hot/power wire touch any bare metal like the chassis. But that's okay since not only will you be mindful not to do such a thing, but you will also disconnect the negative terminal on the battery before you begin.

4) you know how to solder. You may get away with using vampire clips, but you'll have to use your own digression for that.

5) you know how to remove interior panels of the car, get under the carpet, removing your back seats, and the interior panels of your trunk. This is necessary to run wires. It's quite easy if you're familiarly with Subaru's variety of plastic clips.

Although I am quite confident in my modification, and my tech article, I cannot be accountable for people making dumb mistakes, because without question, mistakes will happen. You do have a risk of ruining your entire electrical system attempting this mod as you do with countless others. If you have to ask if this will void your warranty, you might as well close this how-to now, because it no doubtable will. You are attempting this mod at your own risk. If you mess up, I cannot guarantee any support since I as far as I know, am the only person to ever successfully attempt, complete, and post a how-to on a mod like this, although I will do my best to try and help you by chance you do something wrong. If you fry something... well, that's another story.


Soldering Iron
Soldering wire
Crimp Tool
Needle Nose Plyers
Flat Head Screwdriver
Phillips Screwdriver
Something to create heat to shrink your tubing (I used a stick lighter)

Lots of 14-16 gauge wire (when I mean 14-16 in the follow, I mean the gauge, not the amount)
14-16 (blue) F Quick Disconnects
14-16 Ring Terminals
14-16 Vampire clips
14-16 Heat Shink Tubing
Electrical Tape
Automotive Relay

Choosing a Relay
Now I will give you the part number and the place I got my relay from, but what I ordered is more expensive. The reason is because I wasn't sure of the car's logic and needed a relay that acted as both a normally open (NO) and a normally closed (NC) relay. Here are the specs of the relay you need. FYI, SPST stands for single pole single throw, and SPDT stand for single pole double throw. In reality, both will work.

12VDC (give or take 2 volts)
30A (atleast)

The one I got is from, part # Z981-ND
RadioShack one should also work fine model # 275-226
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Last edited by Vew; 09-17-2006 at 02:35 PM.
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post #2 of 7 Old 09-15-2006, 08:02 PM Thread Starter
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Step 0
Remove your ground wire from your battery. THIS STEP IS VERY IMPORTANT. DO NOT SKIP IT.

Step 1
Remove your center console. Open the arm rest, stick a flathead screwdriver under one of the two tabs (use a cloth to prevent scratching anything) and pry. It should pop right off. There will be a wire attached to the power mirrors. Stick your hand under there and unclip the harnass and remove it out of the way. You can probably see your security module now. Next, yank up on the next section around your shifter and remove that out of the way.
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Step 2
Remove your clock. Just give it a good yank, and unclip the wires from the clock
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Step 3
There are 4 wires that run to your clock. If you look at the back of the clock where the clip connected to, you will see it labeled each wire. +12v, Acc, Ilum, and Gnd. You will be concerned with only the "Acc" wire. This wire will only give power when the ignition is on. Tap this wire with a vampire clip and run your extra wire behind the vent, clock, and whatnot, until it comes down to where the shifter is. Proceed to run enough wire to where the security module, making sure to secure the wire along the way so that it does not interfer with anything else (especially the shifter).
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Please note there is an extra few wires in my photo. I also tapped wires for my gauges here, so ignore color wires and go by what the labels on the back of the clock says.
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Step 4
Now Crimp a Quick Disconnect on the end of that wire and you can attact that to your relay's power
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post #3 of 7 Old 09-15-2006, 09:19 PM Thread Starter
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Step 5
Tearing apart you interior. You need to do this to run a single wire from the center console back of the trunk latch. You need to remove the black plastic door sills on the front and the back of the passenger side, remove enough clips that hold the carpet down (front passenger seat) for you to run wire from the center console to the door, remove the black molding underneith the front passenger seatbelt, remove the back seats, remove your trunk carpet, remove the wood board that covers the spare tire, remove the black plastic trim that surround the bottom trunk latch, and finally, unclip and push aside enough interior in the trunk to gain access to the back of the seat.
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Step 6
Run a wire from the center console, under the carpet of the front passanger seat, along the door trim toward the back seat (I used the same path the harnass used), and run it to the top corner where the seatbelt is. If you examine the area, you will see how the factory sent wires through. You can poke wire though that hole and keep pushing for some slack. Run over to the trunk and continue running the wire unti you reach the latch area.

Now notice the two following photos... What happened was I ran the wire, did Step 7, came back and realized I'm an idiot. The wire goes over the seatbelt. Not wanting to resolder connections, I disconnected the seatbelt to free the wire. Just be mindful of things like this that could make your project a headache.
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Step 7
If you examine the latch, you will see a button. If you push on it, the trunk light goes off, and when you release it, the light comes on. That's the switch that signals the car whether or not the trunk is open. My original attempt was to use one of the door switches, rather than the trunk. This way you'd run less wire. However, the side effect is the "door open" light will continue to stay on. The side affect here is only the trunk light staying on all the time, which is okay with me, since I disconnected it anyways.
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Now use a vampire clip to spice into the positive wire. You may need to unscrew it to do this. I can't remember. Anyways, it should be one of two wires that isn't black. The black wire will be connected to the chassis which is ground. As for tapping the black wire, I don't really remember why I did this since I did this mod a while ago, but it works, so vampire clip that too, and attach a wire to the chassis using an eye loop crimp.
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Last edited by Vew; 09-17-2006 at 02:21 PM.
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post #4 of 7 Old 09-17-2006, 02:27 PM Thread Starter
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Step 8
Make your ground 'harness. Technically you don't really have to do this step as it is more work, but I did it to make it look clean and professional. Basically, two of the 4 connections on your relay go to ground. So I made a Y wire so only one connection goes to the chassis. I used the soldering iron for this, heatshrink, the 2 F connectors, and a single eye loop that goes to the chassis.
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Step 9
I tapped the Y connector I just made into ground from one of the bolts holding down the shifter as it was a close and conviennent location.
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If you've done everything right thus far, you should have 4 wires with 4 F crimps on each all comming to the center console. Two of the four wires being grounded to the chassis.
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Step 10
Wire your ground. If you look at the side of my relay, you will see a wiring diagram of the actual relay. You will find something similar either on your relay or on the package it came in. On mine there is 5 connections because it is a SPDT relay (single pole, double throw). Yours should only be a SPST (single pole, single throw), thus only four connections. Using mine as an example, connections 85 and 86 is where power will go. You will connect the ACC wire that you tapped in from the clock onto one of the terminals (doesn't matter what where + and - go), and one of the ground connectors to the other.

The other two you have probably figured out is the acutal switching mechinism. Connect the wire you tapped into the trunk to one, and the remaining ground connector to the other.

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Now wrap electrical tape over the open wires/terminals to prevent any shorts.

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Step 11
Test it. Before you get all excited and start putting your car back together, double check all your connections once more. Make sure there are no loose wires touching anything they shoulding me. Make sure all connections are secure. Now think about what you just wired. Does it makes sense? Should everything work using basic common sense? If not, go back through the steps and make sure you did not acciently skip a step or wire something wrong. Otherwise you can reconnect your ground battery and begin testing.

Get in your car. Turn the ignition on (you technically don't have to start your engine for this). Turn off your ignition, remove your key. Now get out of the car, close the door, and press the lock button on your remote (using the lock button on the door does not work for this mod). Does your car beep (3 times for 02-03 or 5 times for 04+)? Great, now wait for your car to turn off. You should be greated by a single beep to confirm the alarm as been armed. Glance though your window to confirm that the "security" light is blinking in your console.

If everything works, congratulations, you can now clean up your mess, your wiring, cover any open wires with electrical tape, secure everything, and put your interior back together. If not, go through the how-to again making sure everything was done right. It it does not still work. Feel free to post in the Non-Performance Tech section of or private message me on there. My screen name is Vew.

Good Luck!

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post #7 of 7 Old 09-30-2006, 01:04 AM Thread Starter
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The Theory Optional Read

I've decided to add this in case anyone wants to know how it works or is trying to troubleshoot themselves if they run into a problem. I'll try to go slowly... uh, btw, I just realized that I refered to 'door' a lot when I really mean trunk. They both do the same thing. The original mod was modded at the door switch, but that gave a side effect which made me rewire it to the trunk switch.

Basic electricity. A circuit only works when it is complete... what I mean by this is that current will only flow through the wires when it makes a complete loop. When there is a 'break' in the loop, the flow of current stops. When there is a 'short' between two connections (say connections A and B), that essentially means one end of a wire has been placed at point A, and the other end at point B. I will use short and break... so remember what it means!

Ground - Ground is basically the common wire that completes the loop after all the essential items have been connected already. What's interesting, and may be hard to understand, but the entire chassis of the car is ground. The chassis is made of metal, and is used to connect pretty much every since piece of electronic item in the car. Imagine it as a giant wire. You may wonder doesn't this interfere with other electronics in the car? It doesn't. The reason it doesn't is because although yes, every electronic is connected to ground, each electronic item is seperate and is containted within its own 'loop.' Remember that for current to flow, it must be in a loop. Well, current in a loop (say your stereo) can't jump to another loop (say your ECU) with only one common point of origin (ground). It would require two to complete the loop... which would be very bad, and cause a short, and fry both the ECU and stereo. I hope that made sense.

Enough of electricity 101, here's how it works. The factory security system is pretty smart. If you lock your doors/arm the car and you didn't close the door, the system doesn't actually arm until you shut the door... hey, we can take advantage of that.

There is a switch located at each door, and one at your trunk. When the door is closed, the switch is pressed in. This, oddly enough, causes a break in the circuit. This tells the ECU that no current is flowing through the wires, thus the door is closed. When the door is open, the switch releases back out, causing a short. This tells the ECU that there is current running through the wire, thus the door is open.

What the mod does is puts another switch in parallel to the existing switch. Basically, what that means, I step in, and put my own switch in BEFORE the existing switch, so I can override what to tell the ECU.

When your car is on, power goes to the relay, which closes the relay switch. As we know, electricity is lazy. It will follow the path of least resistance... the switch in my relay. Thus, it completely skips the car door's switch, and tells the ECU that there is currently flowing through the wires. If you were paying attention, you know that when current is flowing, it tells the ECU the car door is open.

Now, when the car turns off, power from the accessory wire also goes off. Which means, no power is getting to the relay, and the relay's switch opens back up. This leaves the decision of whether the ECU is told if the door is open or closed to the factory switch. If your door was closed, success, both switches are open and that means door closed to the ECU.

There is a possible of 4 conditions. The conditions, I will be refering in terms of the schematic if you're getting confused. I will list and explain how the relay affects every condition, because you do get one side effect.

Door switch closed, relay switch closed
This means the door is open and the car is on - no problems here since anything the relay affects, should have already happened because of the door being open.

Door switch closed, relay switch open
This means the door is open and the car is off - no problems here because since the relay switch is open, it's like nothing was modded at all.

Door switch open, relay switch closed
This means the door is closed and the car is on - the relay is overriding the door switch, telling the ECU that the car door is open, side effect is trunk/door light is on while you're driving

Door switch open, relay switch open
This means the door is closed and the car is off - no problems here, again, because the relay switch is open, it's like the relay isn't even in there.

I hope that helps with understanding how this whole thing works. If you need clairification, let me know because that means I need to change what I wrote. If one person doesn't understand, that usually means a bunch more don't either.

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