This is essentially ripped from here.
But that page was quite difficult to find and the proper solution is buried within the thread itself.
Full credit goes to bobbych and BillB. I take no responsibility if you damage your radio. Do this at your own risk.
There are other solutions floating around but all of them produced horrible, distorted sound that sometimes only comes from the right speakers. This is the only solution that I found to work on my SC-810 head unit. It sounds very clear and is actually stereo as i believe it bypasses the tape deck, a huge boost in sound quality over the tape adapter I was previously using.
Things:Fine tipped soldering ironSteady hands (Recommend you don't have caffeine the day of doing this)2x 10uf capacitors 1x100ohm resistor (Optional)Aux cord that you don't care about, preferably shielded. I recommend a 1.5m cable for plenty of spare length.Aux to tape adapter with magnetic head and cable removed. (Better than a gutted tape as they have gears to stop the player from auto reversing)Steps:Take your stereo out of the car using the little pull tabsRemove the black back plate/heat-sinkRemove the four screws on the bottom of the unit and pry the bottom plate up.Locate the solder joints to the riser card for the tape deck. (With the radio upside down and facing you it will be a line of joints towards the far left. The first joint on the left will be labelled MS-DET) Find the joint labelled "R" (Right) and follow the trace upwards to a small SMD capacitor labelled 102, there will be two of them, one for the right channel and the other for the left Solder the negative terminal (usually marked with a strip and chevrons) of one of your 10uf capacitors to the right side (output) of the SMD labelled 102 on the right. (The labelling is tiny writing on the component itself, not on the board)Solder the right lead (Usually red) from your AUX cord to the positive side of the capacitor you just soldered to the board.Repeat this process for the left channel by soldering the negative terminal of the capacitor to, again, the right side (output) of the other SMD located to the left of the one you've just soldered to. Again this will be labelled 102. Take your ground wire and solder it to a grounding point on the board, usually a big connection with the case of the radio.
Now you should have both channels connected to the board through your two 10uf capacitors.
Noise issues:
You can also solder a 100ohm resistor in-line with your ground connection as I've heard that helps eliminate some interference.
You can get one of these when you're done if you get electrical noise when driving:
https://www.jaycar.com.au/ground-loop-noise-isolator-stereo-3-5mm/p/AA3086
I wouldn't recommend these mods as they both seem to reduce the bass response significantly. The resistor is less noticeable than the ground loop noise isolator however, so if the noise is really bad in your case use the resistor method.
Works like a charm while driving with no interference.
Should look roughly like this when you're done...
To play connect your aux and put your dummy tape into the tape deck. It will try to play the tape but receive audio from your phone instead. I needed to have my phone above 60% volume for clear audio. Hopefully it works for you ?
