AudiWorld Forums - Connect Cell Phone for Switched Power - Instructions and pic inside (very long)

To everyone that wants to connect their cell phone to their A4 for switched (ignition on) power through the RJ45 connector already in the car, try this out. I did this on my 98.5 A4 1.8t connecting a Motorola M75 digital phone. Hopefully this will be helpful for other model years and phones as well.Note: This will not give you hands free use of your phone. This will only allow you to charge your phone and use it drawing power from the car and not a battery.With MUCH (and I emphasize much) help from Jason who posts on this board (sorry I didn't have your last name) I have successfully connect my phone to my car. Here are some things you will need for this setup:1. A male to male DB25 cable. I chose male to male because it gives you two chances in case you screw the first one up. (I screwed the first one up) Make sure that you get a straight through cable that has wires for all 25 pins. The one I got was for connecting a computer to junction box. One thing to look for is the cable wire should be thick. If you are trying to choose between a thinner cable and a thick one, go for the thick one. You can buy this cable at any computer supply store.2. A RJ-45 cable. Also called an ethernet or network cable. It looks like a telephone wire but the head is bigger with 8 pins.3. Cigarete lighter adapter specific for your phone.4. Some wire5. Lots of electrical tape6. Something that will allow you to check a circuit. This is used to determine which wire in the back of the DB25 cable corresponds to a specific pin. I used a simple setup I made myself. I got a AAA battery and connected it to a light bulb with two exposed wires. I connected one end of the tester to a random wire from the DB25 cable and then ran the other wire from the tester onto the pins until I found the one that lit the bulb. Viola! You have found the pin for that wire.7. A razor blade8. Did I mention a lot of electrical tape? :)Once you got all this stuff you should be ready to start. Here are the steps I went through:1. Cut off one end of the DB25 cable. Leave enough wire to work with, but you don't need a lot. I would say about 6 inches is enough. Cut off the plastic cover (be careful not to cut the wires) until the individual wires are exposed.2. Take the Cigarette Lighter adapter you bought and cut off the lighter connector part from the phone connector part. Remove the protective cover to expose the wires for the lighter connector part first. See how many wires you have. The diagram only shows two wires coming out which is usually a power and a ground. (My adapter had four wires coming out, so don't worry if you have more)3. Going back to the DB25 cable you exposed start testing the wires until you find the ones you need. You will need the switched power, ground, and RJ45 pins. For however many wires you had coming out of the lighter adapter is the number of wires you have to find which correspond to a RJ45 pin. (Make sure you use all the wires that come out of the lighter adapter. They are all necessary. I didn't at first and blew the fuse in the adapter. Then I had to buy a new fuse and delay my install.) Here are the ones I used:DB25 pin 5 (switched power) DB25 pin 3 (ground) DB25 pin 23 (RJ45 pin1) DB25 pin 8 (RJ45 pin2) DB25 pin 11 (RJ45 pin 3) DB25 pin 12 (RJ45 pin 4)4. Once you know which wires from the adapter to use connect it to the lighter adapter. The DB25 pin 5 should be connected to the tip of the lighter adapter and the DB25 pin 3 should be connected to the ground portion (see picture). Connect the other DB25 pins which correspond to a RJ45 pin in any way, just keep track of who went where. One thing that confused me was which is pin 1 on the RJ45? See the picture, that should help.5. Once all the connections are made, wrap it up any way you like. I used a bunch of electrical tape and just wrapped it like a mummy. Jason suggested getting a "project box" from Radio Shack which is a good idea. I got one, but bought one that was too small so I didn't use it.6. Now you are ready to work on your RJ45 cable. Take the phone connector end of the cigarette lighter adapter and expose the wires. Do the same for the wires you need from the RJ45 cable. Connect the wires. Remember to make the same connections you did for the DB25 wire. Wrap up any loose wires and you are ready to fly.7. Go into the trunk of your car and find the DB25 female connector that already exists in your car. If you don't know how to get to it, check the FAQ for connecting a CD Changer. The instructions are excellent. Connect the cables and you are 90% there. (I chose to secure the cable by tying them together. That way it wouldn't come apart when I hit a bump or something.)8. Connect the RJ45 cable to the 8-pin connector in your car (usually located next to the handbrake on the center console beneath the armrest). Connect your phone and enjoy!!Howard Kim 98.5 A4 1.8tms(neu) With a powered cell phone!!