Modulating My Music: An alternative way to listen to an iPhone on an old car stereo

My Camry

February 18, 2012

I love my 2001 Toyota Camry, the most reliable car I’ve ever owned. Its stereo includes both a CD player and cassette deck, and I made good use of the former for a few years and ran mix tapes on the latter until I bought my first iPod for $500 back in 2004. It was amazing to have so much music at hand so easily, but there was the problem of how to get it to play over the car’s speakers since my old stereo did not sport a line-in port like new ones do today, let alone something so modern as a wireless Bluetooth connection.

The cassette adapter I used for years

The first solution, as I’ve noted before, was an $11 Sony SPC-9C cassette adapter, which worked well for years, taking the iPod’s audio out and transmuting it for the car’s cassette player. There was occasional mechanical clicking from the adapter and high-band hiss in the speakers, but the sound quality was fine overall.

My FM transmitter/charger of choice was the Griffin iTrip Universal Plus

The Problems with FM Transmitters

But as noted in that April 2010 post, the cassette player in the car wore out and I had to switch to FM transmitters. I wasted money on three different models until I found the best compromise with my $30 Griffin iTrip Universal Plus. But it was still annoying. I had to max out the volume of the iPhone and set the car stereo to a very high volume to hear the output. Thankfully there wasn’t much hiss, but the sound was muffled and when I’d switch back to the radio my ears were blasted when I’d forget to adjust the volume beforehand.

Worse, with my frequent road trips to go on day hikes, I was always encountering interference from changing nearby radio stations. I’d have to press a button on the iTrip for it to scan for a clear frequency, then dial in the car stereo to the new frequency. If I was in traffic or listening to an audiobook this was a distracting pain and often the iTrip’s selection of a frequency still had considerable interference, forcing me to manually scan the radio frequencies to find one without a station’s broadcast.

So I’ve long dreamed of a car stereo with a line-in jack. But I’m both cheap and very dependent on my car. I haven’t bought an aftermarket car stereo in 30 years, and I didn’t want to pay for a new stereo when the existing one worked fine otherwise. Nor did I want to try and find a reputable installer and then have to make arrangements for transportation while the work was being done. Perhaps I could do this myself somehow?

Feeling Brave

I’d been emboldened by recent success repairing my home furnace and started scouring the internet for options. I quickly learned that my 2001 Camry could be easily retrofitted with an iPod/iPhone port if it had the factory CD changer in the trunk. Er, no.

So that meant I had to open up the dash a bit. I’d never want to take on a full dashboard removal, but my Camry just requires popping out a trim plate to get access to the stereo. I could handle that. So I could buy a new stereo and try to install it myself, but I wasn’t surprised to find there is no universal connection between a car stereo and the speakers and the like. There are all kinds of confusing harnesses and kits to make the needed changes and some folks mentioned still having to experiment with manual wire splices. I hate splicing and my soldering is terrible, so that did not appeal to me.

Modulators versus Transmitters

Then I found out that you can install an FM modulator in your car, rather than the simple transmitters, and get a line-in port that way with no interference and better sound quality. The modulator sits between the car’s antenna and the stereo, directly feeding its own FM signal into the car stereo on a specific frequency when you turn it on. The drawback it that it is much more complicated to install than a transmitter, which you just plug into a cigarette lighter port and hook to your iDevice.

You have to open up the dash, remove the car stereo, interrupt the antenna feed with the transmitter, mount a switch somewhere to turn the transmitter on or off, tap into a live circuit for power and make a connection to electrical ground, and have wires or a port to connect to the audio jack on your iDevice, hide the modulator all of this connects to inside the dash, and then reinstall the stereo.

The Audiovox FMM-100 FM Modulator

It was a lot of hookup for a guy lacking great dexterity, but I spent considerable time reading about the different transmitters compatible with my car stereo, poring over blogs and forums where people wrote about their installation experience. I finally settled on the Audiovox FMM-100, which I ordered for $40 from Amazon.

Side Projects

I was also motivated to go ahead with this project because there were two issues I might also be able to fix if I opened up the dashboard a bit. First off was a second cigarette lighter-style power port, just under the main one, which had stopped working. Maybe I could fix that and have more flexibility in charging devices without using a cumbersome plug-in expander.

I had mud streaks on the inside of my stereo display from an incident last summer

The other problem was a cosmetic one. In July 2011 I tried to visit El Malpais National Monument in New Mexico, but the road was flooded and a police car unexpectedly roaring by sent a huge wave of muddy water all over the interior of the windshield and the dashboard. You can see the mud on the back window – imagine having a bucket of muddy water thrown in your passenger window toward the windshield while you’re driving and you’ll know how I felt. I spent a long time at an Albuquerque Wal-Mart lot cleaning up the mess that day, all except for some muddy streaks down the interior of the stereo display. No way to reach those without taking the sucker apart. Well, here was my chance.


I’m including big photos of each step of the process since similar photos by other car owners for their own vehicles helped give me the courage to take on this project.

The Car Alarm

The first step in opening up the center dashboard console was to get the gearshift away from it. That’s a problem since the interlocks won’t let you put the car in gear without the ignition switch being in the on position, and I didn’t want power to the stereo while I was working. The best thing to do is to have the car off but the key in the on position, apply the emergency brake, put the car into 1st gear, and then disconnect the battery.

Moving the gearshift back

First attempt at moving the gearshift back

I tried that, but my car has a horrible built-in alarm system. I leave it disarmed in valet mode all of the time since I hate car alarms. I’ve even disabled the panic button on my keyless remote because occasionally I’d hit it and the horn would blare and lights flash and the whole miserable mess. I dread when the batteries in the remote or the car itself get old, because that too can cause the alarm system to fly off the handle.

I messed with the car battery to begin with

As I feared, messing with the battery connections set off the alarm, with it blaring away in my garage and annoying everyone on the cul-de-sac, no doubt. They were kind enough to ignore it, as I do all car alarms, but I was still embarrassed. So I opted to leave the battery connected and try a different tack, one which worked for me but which I’m not recommending to you for liability reasons. 😕

Opening Up the Dashboard

I pulled out the coin box to access the fuses and used needlenose pliers to pull out the tiny 7.5 amp one for the radio, checking that the stereo had truly lost power.

I removed the fuse for the car stereo

With the emergency brake on, I pried up the little plastic tab covering the gearshift interlock override. That revealed a button I could push to move the gearshift back without having the key in the ignition.

Moving the gearshift with the interlock override

That gave me enough room to start prying away the trim around the center dash console. I removed the ashtray and then pulled gently but firmly on the bottom of the plastic trim to get it started. Then I used a palette knife to pry away around all of the edges of the plastic trim to release it.

Pry off the trim around the stereo

I then disconnected from the trim the bulb over the ashtray compartment, the bulb around the upper cigarette lighter, and pulled the wires off the lighter socket. I could then look down into the compartment at the lower cigarette lighter socket and, sure enough, the plug on its back had fallen off. That explains why it stopped working years ago. It was no surprise that there were muddy streaks exposed which I could clean up too. I cleaned things up and squeezed my thankfully small hand down into the dash and managed to reconnect the lower lighter socket.

The second lighter socket broke years ago – now I know the orange plug came off the back of it

Removing the Stereo and Inserting the Modulator

There are four bronze colored screws bolting the stereo in. I used a number 10 metric socket to take those out.

Use a number 10 socket to remove the four screws holding in the stereo

The stereo then slid right out.

Slide out the stereo

I disconnected the male antenna plug on the back.

Unplug the car’s antenna from the back of the stereo

I plugged the car’s antenna wire into the FMM-100 modulator’s matching female cord, and plugged the FMM-100’s own male plug into the back of the stereo. This allows the antenna signal to feed on through but allows the modulator to send its own FM signal directly into the stereo rather than having to transmit a signal through the air to the car’s antenna. The interference from other signals also being received by the antenna is the downside of FM transmitters.

Insert the car antenna into the modulator’s female socket, and the modulator’s male plug into the back of the stereo

The FMM-100 can transmit its signal at either 88.7 or 89.1 MHz. The one-page instruction sheet said to pick the one with the least interference from area radio stations, which in my case was 89.1.

Set the modulator frequency to the one with less local interference

Connecting the Power

Now it was time to attach the modulator’s grounding wire. One “live” wire on the modulator has to tap into an existing circuit and to complete that circuit you need to attach another wire to ground – that is, to the car’s chassis. I scanned the interior of the dashboard and found a large pipe running the width of the car high up in the dashboard with braces welded to it which had a few convenient holes. So I stuck a bolt through one hole, connected the grounding wire to it, and used a nut to screw it down tight.

Connect the ground wire to the vehicle chassis

Next I threaded the live wire from the Audiovox box through the dash over to the fuse box where I’d later make the live power connection with the radio fuse connection using a fuse tap I picked up at the local Autozone. It takes the place of the fuse and gives you a live wire for power. I plugged the radio fuse into the tap, but wasn’t paying attention to how I would need to insert a second new fuse for the tap’s live wire. That would cause me some consternation later on.

I used a fuse tap to make it easy to power the modulator with the car’s stereo circuit

Some people like to splice into the nearby cigarette lighter sockets for power, but I wanted to have the box power down like the radio rather than having to manually switch it off to prevent battery drain, and wasn’t sure about the cigarette lighters.

I still needed to install the power switch that came with the Audiovox because to listen to a radio station at 89.1 MHz I’d need to power down the modulator. I threaded the switch on its wire over to the lower dash in the driver well.

Mount the power switch somewhere on the dashboard; I am not good at drilling, so I used a corner of the driver side lower panel

More skilled workers would drill through the plastic for a nice clean mount, but I knew I’d struggle not to muck that up. So I opted to unscrew the lower panel of the dashboard in the driver well, which had one visible screw near the center console, another hidden behind the hood latch, and a final big screw hidden by a plate just above the floor near the door hinge. I then pried loose the top of the panel and cut off a bit near its top right corner so I could have a gap for the switch.  I then used a rubber washer as a backer to help hold everything in place at the junction of several dashboard panels.It doesn’t look great, but it is in an inconspicuous spot yet easy to reach.

Mount the power switch somewhere on the dashboard

That seemingly simple task took me forever, with me fumbling around repeatedly with the big rubber washer, a tiny lock washer, the on/off label plate, outer ring, and dash panel. I finally got it all put together, but I’d exhausted most of my expletives doing so.

As for the live wire, I had hoped that the end of the wire on the Audiovox unit would simply plug into the fuse tap wire, but they were not compatible.

I’d hoped the fuse tap wire would plug into the Audiovox live wire, but they were incompatible

So I cut off the connector on the modulator’s wire, stripped it, and wrapped it around the metal plug on the fuse tap. I left my electrical tape at school, so I used thread seal tape and packing tape. Egad! Many would solder this connection, but my soldering jobs often go astray.

I spliced together the fuse tap wire and modulator’s live wire

I wasn’t ready to plug in for power yet, though. I still had other connections to complete.

The Audio Connection

I threaded the modulator’s audio line in cables down through the dash so they would stick out down below. Unfortunately the FMM-100 uses standard RCA stereo audio plugs, so I need an adapter cable to connect it to my iPhone. Radio Shack sells such a cable but it is rather thick and so is the similar but far cheaper cable from, the best online source for low-cost cables. Whenever you need a cable and can wait for it to be shipped, I recommend you use The above cable is a case in point: 76 cents plus shipping versus $8.99 at the shack.

The FMM-100 uses RCA plugs, so you probably need an adapter cable

I made the connections, but want a thinner cable leading into my iPhone, which I mount on the dash with an Amzer Universal Vent Mount. So I’ll be switching to a short adapter cable and patch cable. I own all of these cables already, having been a technology enthusiast for decades, but the ones I need are at school since I sometimes need them for school-related projects and technology support.

Cleaning Up

I nestled the Audiovox modulator box down in the crowded dashboard. There are so many wire harnesses that it was stable and wouldn’t rattle about.

Find a spot for the modulator to stay inside the dashboard

I reinstalled the stereo, but I really wanted to get those muddy streaks off the inside of the display. I debated whether or not to risk ruining the stereo by trying to take it apart. I decided to go slow and take a chance.

Eager to clean out some muddy streaks, I removed the stereo’s faceplate

So I used a screwdriver to slowly pry off the faceplate, finding to my relief that it had a single large plug connecting it to the stereo cabinet. The front fascia was connected to the display and main circuit board.

A single plug connects the back side of the faceplate to the stereo box

I carried the faceplate into the house for disassembly. A precision screwdriver allowed me to remove five screws holding the circuit board and display to the front fascia.

Five screws connect the circuit board and display to the stereo’s front fascia

I pulled up the circuit board and could then clean the muddy streaks off both the display and the plastic window on the fascia. For seven months I’d had to peer through the mud to see the display; I delighted in introducing the streaks to my friend Windex.

I could finally rid myself of those muddy streaks

I reassembled the stereo, screwed it back into place, reconnected the cigarette lighter socket power and light and the ashtray light, and popped the dashboard trim back into place. Now it was time to apply the power.

Powering Up…Or Not

I slid the fuse tap into place, and those of you who are familiar with the devices will see an error here.

I didn’t realize I needed two fuses in the tap

Unaware of my mistake, I powered on the stereo, hooked up my iPhone, dialed in 89.1, and…heard a distant radio station instead of my phone playing a favorite song. Curses!

I tried the other frequency, hoping I’d just forgotten to switch the modulator, but that made no difference. What could be wrong? Since the stereo worked, I knew the antenna and ground connections were good and the fuse tap was feeding power to the stereo. Maybe the modulator wasn’t receiving any power? The switch was in the ON position, and the label plate is threaded so you can’t accidentally mount it backwards.

So I pulled the fuse tap and examined it, finally noticing that there were holes for a second fuse. Oh, that would make sense. The original fuse should protect the original load and the new load should have its own fuse. I swapped the fuse and reinserted the tap, and sure enough the stereo no longer worked.

Did I have any of those tiny fuses on hand? Of course not, and a survey of the fuse functions on the back of the coin box didn’t show any I could easily sacrifice. So I cleaned everything up and drove to Wal-Mart to get a fuse.


When I returned home I popped in the fuse, inserted the tap, and voilà, crystal clear sound came booming out of the stereo from my iPhone. Good volume, no interference. This project had worked! I tested the power switch and confirmed that it shut down the modulator so I could listen to radio stations at 89.1 MHz if I wanted to.

Now my iPhone plays crystal clear on FM 89.1 whenever I want it to

This was a fun project and I know I will enjoy its benefits for years to come. Not only will I be less distracted and annoyed on my road trips, but I have a cleaner stereo and center console and two working power sockets. Total cost in parts: $40 for the modulator, $8 for the fuse tap, $5 to $10 for adapter cables, $4 for a set of small fuses, a few bucks at most for some tape, a nut and bolt, and a rubber washer. I won’t throw in the $10 for the two lithium batteries I drained in my super-bright flashlight. 😯


Plus labor, but I’m so unskilled that I work for free. That’s much cheaper than a new stereo and I learned some things by doing it all myself. But I had plenty of help from internet posts. The world wide web is pretty wonderful. That’s enough for this post. I’m going to go modulate Mercy, using my iPhone to blast that fantastic song in my car. Crank it up!


UPDATE: I finally traded in my 2001 Camry in August 2014; I had driven it over 236,000 miles. My new 2014.5 Camry XLE has a sound system that automatically connects to my phone using the Bluetooth radio communication protocol. I made sure to leave instructions in my old car on how to use the FM modulator so that the next owner can conveniently connect a smartphone or other music player to the stereo system.

About Granger Meador

I enjoy day hikes, photography, podcasts, reading, web design, and technology. My wife Wendy and I work in the Bartlesville Public Schools in northeast Oklahoma, but this blog is outside the scope of our employment.
This entry was posted in home repair, music, technology. Bookmark the permalink.

2 Responses to Modulating My Music: An alternative way to listen to an iPhone on an old car stereo

  1. Dots says:

    I actually read the whole thing. This, is my next project on my 01′ Camry. Will be back with the outcome. Very well put together, you must be a very good teacher. Your students are very fortunate!

  2. Pingback: A Sinister Mr. Fix-It | MEADOR.ORG

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