The sub-$20 theft-proof stereo installation works pretty well, but let's say your local crackheads aren't desperate enough to bust your windows to steal a factory AM/FM radio, yet they will steal anything nicer? How will you listen to your MP3s?
You can forget all about those wireless FM transmitters, because their weak-ass signal gets stepped on when you're driving in any region more populated than Antarctica. You don't want to run a cassette adapter in a factory tape deck, because intoxicant-seeking entrepreneurs can get 58 cents closer to their next rock simply by hurling a spark plug through your side glass and prying that deck out of your dash (and cassette adapters sound terrible, anyway). What you need, my tunage-deprived friend, is an FM modulator that pumps its signal directly into your radio's antenna input. Don't worry about breaking the bank, because they're dirt cheap!
Some of you may remember my brother-in-law's well-worn-but-completely-functional '88 Toyota truck, which often parks in quasi-sketchy Oakland neighborhoods.
Having already lost a half-dozen tape decks and CD players to thieves over the years, the truck now has a horrible-looking junkyard sound system that doesn't tempt even the most motivated baddies.
We decided on the Boss FM-MOD wired modulator, available for under $25 shipped on eBay. Sure, it's cheap Chinese crap, but it gets the job done and sounds fine.
We're looking at your standard plywood-and-wood-screw mounting system for a separate-radio-and-tape-deck setup from a junkyard mid-80s Subaru GL.
We'll need to get access to the radio's antenna input, so the mounting screws come out.
You need to decide which frequency will be used by the modulator. Since it feeds its signal straight into the radio via a cable, it should be able to override any FM stations. However, it makes sense to choose an empty frequency. Just flip the DIP switches according to the diagram; we're using 88.3 MHz.
If you're using an iPod or other device with a 3.5mm stereo headphone jack (i.e., damn near every MP3 player in the world), you'll need to pick up an adapter cable with dual RCA plugs on one end and a 3.5mm (aka 1/8") stereo plug on the other. These are readily available for cheap on eBay. Plug the RCA plugs into the corresponding jacks on the modulator.
The cable from the vehicle's antenna plugs into the modulator as well; this enables you to get radio reception when the modulator is turned off.
You'll need to install an on/off switch for the modulator, so that you'll still have the ability to listen to the radio. We drilled a hole for the switch, next to the parking brake.
Because so many thieves have sliced up the stereo wiring harness while making off with various audio components over the years, there's a cat's cradle of crazy field-expedient patches and jumpers behind the radio. How about pink notebook paper labels scotch-taped onto wires? Hey, it works!
For the modulator's power, you need to tap into a source of 12 volts that's powered up when the ignition switch is in the "ACC" or "IGN" positions. Not completely trusting in the old labels, I used a voltmeter to test for the appropriate wires. Here we see a nice solder octopus, prior to the application of many layers of black tape; good thing everything is fused!
The modulator comes with a low-quality switch, but I decided to grab a better one from my stash-o-electronics-junk. Power from the wiring harness goes to the switch and then to the modulator.
Before we start buttoning things up, let's test the setup. It's a little more challenging getting the exact frequency with a non-digital tuner, but the sound quality is great.
Back into the dash with the radio!
Zip-ties hold the modulator in place, behind the radio.
Everything is back together and the system works fine. Total cost, including iPod Shuffle, junkyard radio, modulator, switch, and cable: under a hundred bucks.
Ready for the road!