K, first things first. I'm keeping the interior stock. I've had aftermarket units before, but they never look right IMHO, so going that route is off.

I don't want one of those tape thingies that has a wire out of it that you insert in the tape player.

I have the factory radio and tape player without equalizer below it. What's the best way of putting in an auxiliary input? I'd like to connect it to the back of the radio if possible, and know there are some empty spots there. I'm looking to have a female 1/8" (3.5mm) headphone/phono plug coming out the side to connect a wire between my phone and radio.

I'm trying to save having to study the FSM body electrical section lol!

 

^From one of his build threads. Maybe Landon can comment on how he likes their work.
It's on my to-do list, too.

 

Wow lol talk about thorough!

 

Audio Control has a line connector LC6i, LC7i, and LC8i that you can put under your seat and it has an auxiliary input or 2. You can also run a separate amp with better speakers and still use your stock radio with this piece. I have them in my fb and fd. You can put the auxiliary plug in the center console on the front panel and keep it stealth. I did this in the fb.
In my fc I installed a Nakamichi CD400 which matches the black interior perfect(lights too) and is one hell of a head unit. also put a pocket under the nakamichi to fill the dd space. You can get all this on ebay for good prices.

 

S4 and S5 stereos have a DIN plug for the EQ (S4/S5) and cassette deck (S4). It carries the audio, illumination, and switching for the components. You can put an auxiliary input adapter together with a couple of 12V relays (DPDT) , two DIN cables (go with 90-degree ones), a set of RCA jacks a small project box and bit of wire.

I strongly suggest a breadboard and jumper wires so you can test out the circuit before you solder it together.

https://www.facebook.com/media/set/?...5780398&type=3

Unfortunately, I didn't make a schematic, but I took clear pictures of the breadboard--the later pics show the final circuit. Make sure you get the audio ground and +12V in the DIN plug correct; if there's a hum, you've got those two wires swapped around.

The FSM has pinouts of the connectors, but confirm it with a multimeter.

 

You can do all that or make it easy and use this...

Metra 44-FMMOD03 (44fmmod03) 2-Channel, Universal FM Stereo

Sound good and doesn't have issues with interference due to the fact it is wired in. It also turns itself on in the presence of audio signal, so no need to wire in a goofy switch. I install these at work all the time and I have never had a customer complain.

 

A few more details about how the auxiliary box works for an S4 stereo.

One relay switches or "takes over" control from the radio tuner, and the other relay cuts in audio; though you could just dispense with audio cut-in relay and just splice in a pair of RCA jacks.

For example, when you insert a cassette into the stereo's deck, it turns off power to the radio tuner. The preamp and EQ get their power through the 12V in the DIN cable. The "take over" relay coil gets powered from an external +12V that can be shared with the 12V on the stereo's 1/4" terminal and you can tie the relay ground to a switch or ground-output from a Parrot bluetooth unit. Alternatively, you can flip the coil's inputs around and ground one side to the chassis and use a device's 12V output trigger to cut-in.

Actually, now that I think about it, you don't need two relays, just a SPDT (single-pole, double throw--not DPDT as previously posted) for the power cut-in relay, a small breadboard for soldering, two RCA jacks, two short lengths of 18-awg wire., two small-gauge DIN8 right-angle connectors and a (smaller than original that I used) project box. The wiring shown on the breadboard in that link I posted still applies, just minus the DPDT audio cut-in relay.

 

That is also an option, though you could face the issue of multiple radio broadcasts interfering with the modulator.. The radio tuner on the S4 stereo seems clean and sensitive, though I fiound the preamp seemed pretty decent by itself too.

BTW, you can either wire in a simple switch, a 3.5" jack that grounds the relay coil when a plug is inserted or tie in a device with a trigger output.

 

Nope, it tags in between the radio and antenna. There is no interference at all.

 

Some great options guys. Thank you all.

(If anyone else has more info or options, post up so this becomes great reference info)

 

Well, there you have it. Buy components and build and go through the preamp, or buy a moduleator and go through the radio. I'd say in day-to-day use, you'll probably notice little difference with the factory stereo.

 

No need to reinvent the wheel. JJwalker gave you the best, simplest and probably cheapest option. All you need is a FM Modulator. They have been used for years, remember the CD changer craze back in the early 90's? Every single vehicle with an OEM radio and an aftermarket CD changer, had a FM modulator.

Works, and its cheap

 

Oldest trick in the book... Cassette tape adaptor.

http://en.wikipedia.org/wiki/Cassette_tape_adaptor

 

^
I do have an FM modulator also from a Pioneer CD changer that I sometimes use. Gotta check if it has the right inputs.

 

The old Sony and Kenwood FM Modulators had an RCA input for the changer conection. If your Pioneer modulator is anything like the two brands mentioned, all you will need is a mini plug to RCA cable.

 

I had an fm modulator at one point in highschool, and threw that thing away. Awful sound and fuzz. Maybe they are better now. But whats wrong with inserting a damn tape? It will literally take 2 extra seconds and cost $3.32 new.

 

I get that the OP is looking for a clean install with no goofy wiring hanging all over the place. That was my exact motivation. More, the problem with FM modulators is you cut the highs and lows of your music since it's running through the radio antenna. So no "CD quality" listening.

Clousborne is on track to the simplest and least expensive approach to get direct wire input to the head unit so you don't loose those highs and lows. I did this to my S4 Vert more than 15 years ago, have never had a problem with it in all that time, and was an easy retrofit since the S4 has a component skip happy CD player that I eliminated. What I'm about to describe can also be done with the S5 head unit despite CD and Radio are one unit so no separate DIN input like the S$ has. You have to open it up and get very creative to make the same connections to the places I'm about to describe. If you're intimidated digging through the head unit, the FM modulator is the only way you should go for the S5 head unit in my opinion.

The DIN connector provides 5 key connection points, Left channel +/-, Right Channel +/-, and a negative trigger. As background, when you push in a CD the factory component CD unit, it sends a negative trigger to the head unit telling it to look to the CD DIN connection point for audio. So the single pole switch simply tricks the factory head unit to look to that DIN input.

What I did was go to my electronics supply house and purchase a standard male DIN plug, a single pole single throw switch (for the negative trigger), and a double RCA output 6 RCA jack input A/B/C switch since I wanted to add three components. An XM radio receiver (I chose the old school Sony device for a secret reason), a trunk mount CD Changer (also went Sony), and most recently a Blue Tooth A2DP device. Now days I would expect most would just add the A2DP device and be done. This most recent addition allows me to get legal with hands free use of my Smart Phone that I can actually hear the caller since it utilizes the factory speakers (most important my Vert Headrest speakers) and at the same time allow me to stream smart phone music/GSP instructions that play through those same factory speakers. There are a number of A2DP devices to choose from, I went with the Belkin unit.

So, to recap, all you need is a DIN plug, Single Pole Switch, and multi switch that has two RCA out jacks and enough RCA jack inputs needed for however many components you want to add, perhaps 1 or more mini-phone jack to RCA adaptors, some wiring, solder, shrinking tubing, and patience to do a clean job running the wiring for it all.

Anyone attending my Puente Hills meet this Saturday, ask and I'll show you my install.

 

As mentioned earlier I sent my radio in to factoryradioservice.com (yes I am very thorough hahaha). It's been a year & a half later, the car's garage kept & has about 1700 miles of use on it since. Everything still working great (CD, Cassette, radio, all speakers, aux input) with no hiccups of any sort. Definitely recommend!!

 

Dude, did you even read?

DIRECTLY WIRED FM MODULATOR IS PUT BETWEEN THE VEHICLE ANTENNA AND THE RADIO. What this does is, when it broadcast, it broadcasts directly into the radio AND NOT WIRELESS!

Thought the caps may help you read better.

 

You get some noise from the tape mechanism (motor/pulley/belts) when using it. Not sure if that happens with everybody.