How to hack an AUX input into a Delco tape deck for $10

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.

Tools/equipment required:
7mm socket and ratchet
5mm socket
soldering iron and supplies
wire
shrink tubing
assorted drills
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.

Here’s my radio:
(Ooh, look at those fingerprints! I really need to detail the poor truck.)

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.

26 comments

  1. George

    This is exactly the hack I was looking for. Thanks for pioneering for the rest of us.

  2. George

    This is exactly the hack I was looking for. Thanks for pioneering for the rest of us.

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  4. Mark Scudder

    Thank you.  I have a deck in an ’02 LeSabre that has a bad tape head that seems to “sum” everything to mono, so the cassette adapter I was using wasn’t providing very good audio, and as you said, the FM modulators are underpowered garbage.  After spending two days trying to jack in to the circuit at points in the tape deck module – somehow the tape head was still part of the circuit and was summing even external signals – I ran across your blog post when I was about to give up.  I had a feeling two of those wires sent clean, line-level left and right back to the amps, but I didn’t know which ones, and I didn’t feel like blowing up my iPod if I accidentally touched it to the 12V line in my search for the right wires.  But you found ’em.  I got a patch cable right in there, and it works like a charm.  One thing, at least on mine, if you get a thin stick and use it to push on the vertical plastic piece that the tape hits when it goes in the deck, there’s a good chance it’ll just engage the mechanism and think there’s a tape in there, forever, which allows you to switch to the tape source anytime you want, without having a tape in there.

    I should also mention I had access to the deck out of my father in law’s old ’01 LeSabre, which worked perfectly fine with the cassette adapter, but thanks to TheftLock II, despite the head unit fitting in my dash, I couldn’t make it work.  GM needs to get real with this Theftlock crap.  Nobody steals factory head units anymore, and the professional chop shops that do deal in black market car parts have the means and the money to get their hands on the $3,000 “Tech II” computer that can reprogram the decks and defeat Theftlock.  So it appears that the only people really hurt by this technology are honest consumers like me, who in a bad economy find a better way to fix things.

    Thanks much for your post.  You saved me a lot of money, a lot of frustration, and helped me win one against a real cluster.

  5. Wayfastwhitey69

    call me dumb… but how do you know which pin is which? what end do i count from? lol

    • mack505

      Pin 1 is the striped wire.


      James
      The optimist sees the glass as half full; the pessimist as half empty. The engineer sees the glass as twice as large as necessary

  6. Wayfastwhitey69

    ok, im offically stumped. ive spent the last few hours trying to figure out whats what on this jack but i cant really find an answer. i have no clue how to read the diagram on the back of the jack he said to buy. here is a link to a picture i took of the back of the radioshack bag. if someone could please explain what goes where i would be eternally grateful lol.

    http://i266.photobucket.com/albums/ii274/eltatertoto/audiojack.jpg

    • mack505

      From looking at your pic it would appear that pin1 is common, Pins 2&5 are left and right signal, and pins 3/4 are the normally closed ones you would use if you wanted to keep the tape deck functional. I don’t know which are left vs right. It doesn’t really matter. HTH.

      • Wayfastwhitey69

        thanks alot. i had pretty much determined that myself looking through the clear plastic window on the side of the switch but its nice to have confirmation. 

  7. Wayfastwhitey69

    how do i determine which is left and which is right? sorry for spamming the post. 

  8. Hakon

    Nice, but would it not be better to hack the radio, so that the tape player does not have to run all the time, just in vane?

    • mack505

      As I said, that could be done with a relay located in the proper spot. I didn’t take the time to find the proper spot.

      If you locate it, please LMK and I’ll be happy to add the information.

  9. Wayfastwhitey69

    just an update for me… still working flawlessly. we take advantage of the jack and use it while streaming netflix from my phone on the long 9 hour trips from memphis to chicago and back. other than my acdc tape from the 80’s needing to flip every 45 minutes it works perfectly.  one hangup i have found is that the charger when the phone is close to dead makes an annoying hissing interference noise. any idea on how to isolate it? thanks alot for making this write up. 

  10. Caleb Reininger

    I have a question. Would this hack work if you only have a CD player and not a cassette player? Could you still perform the hack on the CD player wiring and have it still work? I have been struggling for some time to figure out how to play my iPod through my 2000 Pontiac Bonneville’s factory radio.

  11. Tristan

    Wayfastwhitey69–the hissing noise when you plug in the charger is from ground loops. You can buy a ground loop isolator from Radio Shack for $20. Wire that in and it should be fine.

  12. shashit K

    I tried it getting the left audio and some distortion on the right … can anyone help me please!!!

  13. Dougie Quick

    Very nice hack you outlined here and tantalizingly close to my needs … my 03 Avalanche stereo looks SO similar except it lacks the tape deck! But I am assuming I can do the same thing using the CD player connections? I would like to keep the cd functional of course. I’m not brave enough to finger this out for myself so hopefully I can find you hack adapted for the same system minus the tape deck. Thanks so for the inspiration! I am encouraged now! Anyone know where I can find this info? Delco stereo I think ..looks so close just no tape! Has the “band” button and all, two connectors on back etc!

  14. Noah

    For some reason, my unit won’t stay selected to tape. I get nothing for the brief amount of time it switches to tape, then it goes right back to the radio. Any ideas?

    • mack505

      Did the tape deck function properly before the mod? My only thought is that the Delco tape decks require a regular tape to function properly. If you use an endless loop or if the tape breaks, the tape deck will turn off. Both spindles must turn. (I have an old Meatloaf album perpetually spinnng in mine.)

  15. Chris

    Trying this once my replacement cassette deck arrives. For those of you with this radio, mine was part no. 09376303 and i got it at replacement radios.com. apparently it’s brand new. kept getting the Check Tape error, tried everything (new cassette adaptor, tried regular cassette, tape cleaner) and finally said screw it and took it all apart. Not sure what is wrong but should be all set once the deck arrives. Worst case if i mess up i can just order another deck.

  16. Chris

    Mack (or anyone) – any idea if the audio jack sounds better than using a cassette adapter? Just curious