BMW Sport

1) 2008 models and before actually have key lock on the trunk - it's hidden above the license frame. This would have been great, but I have a 2009, so I don't have one.

2) Some models have a trunk pass through which would allow access through which you could pull the manual release within the trunk using a coat hangar or something. My doesn't. (I also spent some time trying to remove the seat backs, but I don't think I could have gotten them out without breaking something because the latches held them in place so securely.)

3) You can apply power to the car from the engine area -there's a big red + and a ground point nearby. Once power is on the car just push the trunk release in the driver's footwell. This is almost certain to work for most everyone. I'm not sure why it didn't work for me, but I'm guessing it has something to do with the fact that the battery was completely removed and the cable were lying loose. That was strike three - I felt like I was out.

4) The only solution that worked for me was to run down the wiring diagrams and locate the "central locking drive, trunk lid" that's the solonoid that actually releases the trunk. Most of the effort was getting the information - the job itself was actually pretty easy. Here it is:

a) Take out the two torx screws just below the glovebox on the left and right to remove the panel below the glovebox. Disconnect the power socket and the light which are attached to the panel.

b) Below the fusebox there is a big flat horizontal junction box (Junction Box A4010). You can spot it easily because there are two big connectors going into it facing you. There is a flat wide connector plugging into the BACKSIDE of this same junction box. There are about a dozen small wires going into it and one big brown ground. This is the one you need to get to. (Connector X14270) Ideally, you'd want to disconnect this, but I could not manage to get it out from that position.

c) Identify the small wire which is gray with a stripe of green (it looks mostly gray). If you get the connector out, this is pin 12. It's the only grey/green wire in the bunch though.

d) You need to very briefly apply 12 volts to this lead to pop the trunk. I did it the ugly way - I very carefully razored off some of the insulation to expose it. Then I just attached some leads to my new battery. I stuck the ground lead into brown wire connector for the power socket I had disconnected when I removed the glove box panel. Then I just brushed the positive lead against the exposed pin 12 wire. The trunk popped instantly.