Aux Input for an Older Delco Radio

I tried to post this last night, but for some reason it didn't work.

Hello. This is my first post here(second now). I've been all over the internet and joined at least half a dozen groups and cannot find out an answer to this. I have a Delco am/fm cassette from a 1988 Chevrolet Celebrity Eurosport VR. The model number is 16041264. Servivice Manual 2H. Its a regular ol' factory stereo from any number of late 80's GM cars. I want to put an AUX 1/8(3.5mm) stereo plug in it to play my iPod through. I have 2 of these stereos torn apart on my workbench right now that I've been tinkering with for quite a long time.

I know this can be done as there is now a person on ebay selling the modified radios with the input plug. Here is his description : "It has been bench tested with all repairs being made as needed, including replacement of all burned out illumination bulbs. It then had a 3.5mm aux input jack installed in the faceplate, which is a direct link to the amp, with all new electrical connections soldered inplace for dependability. The unit now has the ability to play virtually any portable music device which features a headphone jack and without having to rely on a fm transmitter cassette adapter, or dummy cassette. All of the radio and tape functions perform just like a stock unit and work perfect as well as the control knobs and buttons. Here is how the aux jack works. When you put the 3.5 mm plug into the jack from your IPOD, MP3, or portable CD player, it cuts the radio signal going to the amp. Which allows the signal from your device to play through the radio's amp and then to your speakers."

I'm assuming he's cutting the feed from the radio and replacing it with the feed from the 3.5mm plug at the cassette deck. Thereby fooling the amp into thinking its being fed by the cassette signal. I figured out how to cut the radio signal, but can't get a signal from the mp3 player. There are 5 wires connecting the tape deck to the rest of the stereo RD, R/W,BRN,OR,and W. I put a switch in the red wire. That cuts the radio signal going back to the amp in the RED / white wire. I spliced into the other 3 wires with a 3.5 stereo receptecle. When the switch is thrown, it cuts the radio signal, and should allow the mp3 signal to pass to the amp. Should being the key word.  So I put the switch in the R/W wire. Now I get a signal, but its overpowering the amp. The speakers only "thump" the bass line of a song.  So I then put some 100uF caps on what I think are the 2 channels from the iPod that I spliced into. The music is now there, but is weak, and I'm getting noise from the tape head I believe. Heres some pictures if that will help.

This has GOT to be a simple mod, but I have absolutely no experience at this stuff, nor proper equipment. Ideas?     Anyone????

I have never attempted this before..probably because the mp3 technology is relativly new..so no real demand. Basically I am in the business to install and SELL. So if a unit comes in that is not compatable..it is an easy sale to upgrade to a unit with mp3 inputs instead of modifying a 20 year old delco tape deck. However, on a newer model with a nicer head unit..it might be something worth attempting..we all know how lousy FM mods sound.

But, I respect anyone willing to perform custom unique stuff and will tell you how I would attept this.

ok..we know a tape head adaptor works. So all we need to do is connect to the tape head left and right audio signal wires behind the tape head..and somehow get the head unit to switch to tape mode.

Try to find the wire(s) on the switch that switches the deck to tape mode and check with a meter what signal is on the wire(s)...don't forget to ground the shields or expect hum. If you can't get it to switch to tape mode by using the plug itself..install a switch or relay..or perhaps you can modify an exsisting switch or button on the delco to perform this function. Seems simple to me. I had a delco lying around but I just installed it into one of my old cars I am selling.

Next delco I come across (I do often but usually toss them out..have no real use) I might attempt this myself for giggles. If I can get it to work before you do I will post back what I find.

Best of Luck and keep at it.

You are on the right track with your approach  the only problem I see with Master's plan  is that the cassete head has an output in the microvolt range and you MP3 has probably about 1 volt  output.   We will have to find a place to tap in after the Head amplifier,

I will look around at work to see if I have a deck of this type and will post tonight.

If tapping off the tape head was a problem why do the casette adaptors? Regardless, if there was an issue with too much input voltage we could take the guts out of an adjustable LOC (or maybe just a simple resistor)and put it somewhere inside the head unit..theres really to much to them.

Theres no real guarantee that doing after the head amp will not have problems either..and then finding a way to switch the source as well..but I do agree that is another approach..I was looking for the simplest way that has no reason not to work.

Hey thanks for the quick replies! Had no time to mess with it tonite, and a friend is loaning me digital multimeter tomorrow. You'd laugh at my rinky-dink multimeter I've been using for this. I agree that it should probably go thru the tape deck somehow. I'll post some more pictures tomorrow and a little more of what I've learned in this adventure. Thanks again!

OK, Heres some pics. These are showing the cassette deck and underside of the board on it. The red (R) wire sends a signal or power to the deck and the radio. The red and white(R/W) wire returns a signal to the amp. On the microswitch, the R is on the (G) terminal. R/W is on the (NC) terminal. The R/W wire is connected to nothing else on the board or harness. When the switch is thrown, the R/W is disconnected, the radio quits, and power is sent to the deck thru the (NO) terminal. I spliced into the 3 remaining wires. I think that the brown(B) wire is a ground, and the orange(O) and white(W) are the left and right channel positives. Haven't figured out which is which. If I trip the switch manually,no tape inserted, it cuts the signal and allows music from the CD player to pass thru. But ONLY if I have the 100uF caps on the channels from the spliced in wires. Are you still following me?........ No caps and the signal is too much, and it wont play, it just thumps bad. And I get the hum. And some of the radio sound. With these caps the signal seems to be a tad too weak.

I'll mess with it some more and post back soon!

and no digital multimeter tonite, the weather here turned bad(St.Louis) so my buddy didn't come over with it........

WOW!!!! lets try that again..............

when I stated "checking signal" I was refering to + and/or - voltage for switching in and out of tape mode..not audio. If you do not have access to an o-scope for signal you can do it "trial and error" method by hooking the unit to a test bench and sending an audio signal to random wires from the tape head that have previosly been verified as not having voltage or ground. The leftover wires must be audio as there is not that much to a tape head. You will hear audio when you are on the right wires.

I do not have access to a o scope so thats out. And I'm getting sound from the O,B, and W wires. The spdt switch and the n/c switch are one in the same. You're just looking at the 2 sides of the board. My terminology might not be too good. The R and the R/W wires from the harness end up at that switch. R on the (G) terminal and R/W on the (NC) terminal. Yes, the switch is opened when a tape is inserted, killing the radio. The R/W wire goes to nothing else on the board. It goes back to the radio. So I'm assuming the remaining 3 wires are carrying the cassette signal. And I think B(brown) is the common or ground.

When I trip the switch with a jumper wire across the G and NO position the cassette mechinism fires up, the motor starts, and it acts like there is a tape in there but there is not. I can then get sound from the CD thru the spliced in wires. But I'm also still getting radio sound at the same time (along with the hum from the tape head) because the switch has not been moved physically from the NC position. Somehow that switch has to be thrown without actually putting in a tape. And I need to know exactly which wire would be the ground for the CD headphone out.

Can't figure out how the guy on ebay is doing this. He's done it to many different Delco radios from the early '80s to about '97. There has to something in common with all of them. A stereo headphone plug, a couple of wires, some solder here and there.

We had quite an ice storm here last nite and the power is still out. Might not get it back for several days! And is gonna get down to 15 degrees for the next 3 nites. So any experimenting at my end is on hold.

Ice storms? I remember those. Now I live in hurricane ally. No ice but plenty of rain and wind. and long power outages so i feel your pain.

This is a tricky one since i do not have a delco tape deck to experiment on at the moment..but as I stated if a casette adaptor works (you might want to actually try one) and the levels are good with no "hum"..you should be able to do it through the head wires in all logic. as far as the switching I know it uses a mechanical switch..this would be much simpler if it was a full logic deck.but not so.

However, to do it this way (I have no idea how the other guy does it.he might be a delco engineer for all we know...or very lucky..lol) we would need to "mimick" everything the wires from that tape switch do or expect problems.

Keep us posted once everything thaws....best of luck.

Well I wish I knew someone with those skills and electrical knowledge. I have asked just about anyone I can think of, and this is where I'm at! But I'm not afraid to learn. So just bear with me on this...I really want to figure this out.

I'll look at the 'Shack for some "pots". Should I get 3? or 2? And as long as I'm there....Anything else, as far as parts, that I should pick up?

Ahhhh....thats a cool idea! I'll see about that.

Got the power restored about 3PM today, and picked up the multimeter. Its a FLUKE 87 True RMS Multimeter. It looks most impressive! My buddy showed me how to do a few things with it, so we'll see if I can get it to work.

Well my radio gave up the ghost tonite while fiddeling with it. Puff of smoke from the amp area. I did get a breadboard and got it hooked up.I just cut up a cassette harness and put the board in the middle, and then ran a ground between the radio chassis and the deck. Sweet idea, geepherder!!!  Tomorrow I'll swap in another amp that I have here. Don't know if its any good either! If not, then its off to another junkyard!

I got a stereo volume control potentiometer while I was at the 'shack today, 100k, and some 47uF capacitors. But I never made it far enough to put them in and experiment. 

I'm at a standstill....... again :(

Heres a couple of pictures of the test set-up.......

Yeah this sounds like what I reccomended to do way back in the beginning of this. I saw no reason why that simple "hack" method into the tape head audio wires and using a switch to "trick" the unit to thinking a tape was in it shouldn't work. However I did always wonder why anyone would really want to do this to a delco as there are many aftermarket decks out there with aux inputs as well as ipod interfaces very fairly priced that would sound alot better then an old delco.

But regardless if for some reason someone was really attached to an old delco we see it can work if sound quality is not a concern.

Hey guys, I did get the radio from the guy on ebay. Got it all figured out now. The tape deck is NOT the way into the amp for this mod. I have improved on his method and I am now selling the complete radios and input "kits" (with detailed instructions) on ebay myself. Its a very simple mod. No switches. No tape adapters. The radio and tape deck work normally. This will work on 90%  of GM Delco radios from 1982 thru 1999. Do a search for "delco ipod"  on ebay and you'll find them.

As for why I would do this?  I want to retain the stock look of the interior of the car. The aftermarket radios never fit in the space without adapters, and I personally think they look like crap. The headunit itself sounds just fine, and with an iPod hooked up directly to the amp, its CD quality!