I wanted a way to use my mp3 or phone to play music through my stock radio, I don't like the sound quality of FM transmitters and I had a budget of 20 cents!, I searched online for any mods to add Aux-in to my 98 wagon head unit but I couldn't find any, so i had to figure it out myself The idea is not mine, it has been done before but I couldn't find any info on our stock radio, and to make things worst Ford uses their own name coding for all chips inside the radio so you can't really tell what those chips are! it's like they are trying to keep us from understanding how their state of the art radio works just makes us feel a bit more special Warning: if you don't have basic soldering skills or don't know how to handle PCBs this project is not for you, I won't be held responsible for any damage. We are going to tap into the radio output on the board with a phone jack so whenever you connect any 3.5mm stereo plug to that Aux-in the audio from the radio will be disabled and the external audio source will go directly to the head unit power amp, if you want to hear the radio just remove the 3.5mm stereo plug from the jack It would have been easier to use the tape circuit as the audio wires run in a flat cable to the board but that meant I have to run a Tape in the head unit all the time which I didn't like, after all it's 15 years old device, so I choose to use the radio circuit which made it a bit more difficult. This is not a complete guide, if you don't know how to remove the stock radio I'm sure you'll find that info with a quick search. Tools required: 1- soldering iron and some solder 2- cutter or x-acto knife 3- 1/8 stereo phone jack from Radio Shack part number (274-0246) 4- some hook up wire 5- T10 and T15 torx screw drivers 6- drill with a 5mm bit Steps: 1- Remove radio from dash and remove the A/C control knobs, front face plate, top cover and tape mechanism until it looks like this: we will be working on the two traces on the bottom right 2- This is a close up of the two traces that carry the radio right and left audio channels: 3- using your cutter or x-acto knife very carefully scrap about 1/2 inch of the green coating on the board along both traces to expose the copper conductors then cut the traces in the middle of the exposed area ( if you don't know what you're doing leave this to someone who does, you could easily ruin the whole board) now add a bit of solder to all the exposed traces making sure you don't join them again where you cut them, you now have 4 contact points (2,5) on one side and (3,4) on the other, you will figure out why i gave them those numbers in the next step 4- cut 5 equal pieces of hook up wire (about 6" each) and solder them to the 4 points and any of the two grounds on the board , on the other side solder them to the audio jack, point 1 on the jack goes to any GND , point 2 on jack goes to point 2 on the board and so on.. Phone Jack pin-out 5-choose where you want your Aux-in jack and drill a hole and make it fit snug. or you could even use audio shield cable and have that connector hanging in your glove box or anywhere..