I’ve searched high and low for this information, and I couldn’t find it online. After I figured it out myself, I thought I should share. A recent annoyance with our cars has been the lack of AUX-in jacks for my iPod/iPhone. I’ve experimented with RF modulators, and I hate them. None of the ones I’ve tried perform as well as I think they should.
So the goal was to have a headphone-style input jack in each car. I don’t care about controlling the iPod or charging it, just getting the sound into the radio. Last month I did the conversion on the C240; it was already well documented on the internet.
The donor GMC is a 2004 with CD and tape deck. It does not have satellite or changer controls. (There are products on the market which will fully integrate an iPod with a radio which has changer controls. They cost a lot more than the $10 I spent.) In the 5 years I’ve had the truck, I’ve never put a cassette in the tape deck, so I figured that would be a good place to start. As it turns out, I can keep the tape deck functionality as well.
7mm socket and ratchet
soldering iron and supplies
Radio Shack #274-246 1/8″ Stereo Phone Jack
1/8″ to 1/8″ stereo patch cord
Before we go any further, I have to do the disclaimers: This worked for me, but I make no guarantees. Make these modifications at your own risk. If you are comfortable installing a car stereo or a set of fog lamps, you should be able to do this hack. If you fry your radio, your iPod, or your car, I take no responsibility.
If you’re OK with the risks, read on.
Start by disconnecting the ground terminal on the battery. This helps keep you from frying things or blowing fuses.
Remove the dash panel surrounding the radio, A/C, and speedometer. This should just snap off.
Use the 7mm socket to remove the three screws holding the radio. Slide the radio out and disconnect the antenna and multi-pin connector from the back. Take the radio inside to your workbench.
Pry open and remove the bottom panel of the radio. You should see the bottom of the tape mechanism. Remove the (4) 5mm bolts holding the tape deck, and turn the deck over.
At the rear of the deck you will see two multi-wire connectors running from the tape deck to the main board of the radio. You are interested in the smaller, 7-pin connector. Snip the wires connecting pins 5 and 7 to the main board. Snip them midway between the board and tape deck to allow room to work.
Decision time: if you don’t care about using the tape deck, you can solder the wires from your 1/8″ jack to the wires coming from the main board, and tape up the ends coming from the tape deck. If you want to retain the cassette, run another set of wires from the normally closed terminals of the jack to the tape deck.
Seal all of the connections with heat shrink tubing. Route the wires out through any convenient hole in the radio case. Connect the ground wire from the jack to the case of the radio. (I used one of the 5mm screws holding the tape mechanism for a ground point.) Close up the radio and head back to the garage. Reconnect the multi-pin socket and antenna, and mount the radio back in the dash.
Locate the jack on the dashboard, drill a suitable hole, and mount it. I located mine above the airbag cutoff switch. Reconnect the battery and test everything before completing reassembly of the dash.
You will have to put a tape in the cassette deck to make this hack work. If you’ve kept the deck wired in, it should work normally. When you plug the patch cord into the jack, the signal from the cassette is cut out and replaced by the AUX-IN signal.
That’s it. It took me less than 2 hours, including determination of which wires to cut.
If your radio is different, you can determine which wires to cut using an old pair of headphones. Cut off the plug and strip the wires so that you have one positive and one ground. (It doesn’t matter which side.) Play a tape. Touch the ground wire to a grounded part of the chassis, then briefly touch the other wire to each terminal. You should hear the signal from the tape deck on two pins (left and right.) BE VERY CAREFUL, as you will have to operate the radio while doing this step. You could zap yourself or your radio if you are not careful.
Further refinement of this hack could include finding a way to fool the radio into thinking there was a tape in the deck. I’m sure it could be done with a relay installed at the proper location, but I didn’t take the time to locate the right spot.
Remember, you are on your own for safety and liability. Good luck and happy listening.