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Difficulty: 2/5
Introduction
Congratulations! You just finished the keyless entry retrofit! Now why won't it open the trunk? You have additional splicing to do. If you can live without the trunk button working, just leave it alone. Otherwise, read this article below. Note that you have to have the trunk release solenoid already in the car to unlock the trunk. In other words, the station wagons do not have this capability, since only the sedans have the solenoid and levers, etc. that are in the trunk.
Parts
Phillips screwdriver, #2Procedure
First, disconnect the battery.
Remove the dashboard cover and the keyless module.
Remove the center console to get access to the console-mounted trunk release button. Review this linked article for any questions about 1000 answered questions: removing the center console on an mk3.
Find Pin#1 on the 10-pin connector on the alarm. It should be red/white and have 12V but check, refer to the circuit diagram on the alarm installation page to find the correct wire. Cut it and put electrical tape or wrap the end so it doesn't ground out.
Run a wire from the alarm to the console trunk switch. Start feeding some of your 18 gauge wire where you just cut the alarm wire. Route it under the steering column, and towards the radio and climate controls. Secure it with zip-ties to keep it out of the way. Finally, route it down to the floor and along the tunnel, ending up at the trunk switch wiring. Cut the wire at both ends, leaving a little slack to allow for putting the alarm back in place later. (better too long than to short, right?) Strip a little off the ends so you can connect it in the next steps.
Use a crimp connector to attach your newly-run wire to the red and white wire you cut in step 5. You now have pin 1 on the 10-pin alarm plug connected to the free end of your wire at the center console. Use a multimeter to check this continuity.
Carefully remove a few inches of the electrical tape wrap around the three wires of the trunk switch. Here's what the three wires do: Brown, ground Gray, to trunk solenoid Red/white, 12VCut the gray wire in the middle of what you've unwrapped. Leave a couple inches on the switch side, and a couple inches on the half that runs to the trunk.
Time to connect the relay. It has five terminals, and if you're lucky, you've got a harness with it to make wiring it up easier. You're going to connect those 5 terminals to the 4 wires you have at the center console (both halves of the gray wire see some action) Connect the wires as follows: Make sure you leave plenty of slack, because your relay and trunk switch may be several inches apart when you put it back together. And wrap your connections in electrical tape when you're done.
Pin 85 to the brown wire using a tap-in connectorNext, you want to secure your relay to something. Since the relay I bought had a mounting tab on it, I drilled a hole in the metal bracket that holds down the e-brake cables, and used a screw to hold the relay to that bracket. You just have to be careful about placement, because if the relay is in the way, you might not be able to put the console back on right. Alternatively, you may want to Velcro the relay to the inside of the console or something. I'll let you use your imagination for this step...and of course, putting the relay at the fuse box would avoid this all together.
Reassemble your console and dash. It's all just the reverse of disassembly. Don't forget to reattach the connector for your trunk switch. When you're done putting everything back together, reconnect your battery terminal, and you're done!
Test out your new feature. Pushing the trunk release button on your remote should cause the same "ka-chunk" sound from the trunk that you get when you press the console button. Also, if you did everything right, your console button should still work as it did before.
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