1999 Mercedes Benz ML430 Repair Question
Mercedes Benz ML430 Radio Problem
Aftermarket radios generally don't use those silly unlock codes. If the display is on and shows the radio is tuning in a station, it is working. There was likely a remote amplifier as part of the original system. It will either need a turn-on signal from the radio or it will need to be bypassed.
I don't know how they use amps, assuming they do. Chryslers can have aftermarket radios installed with or without their original amplifiers and any radio will work fine. On most other brands, when they installed an amp, the original radio NEEDS that amp to develop normal volume. On those systems you can't use those amps with aftermarket radios that run speakers directly. Many high-end radios also have "line outputs" that do require a separate amplifier.
First you have to determine if there is an amp in your car. If there is, there was a wire from the original radio that sent the turn-on signal to it. If that signal was just a switched 12 volts, your new radio will have that wire. It's usually blue and will be labeled "amp", "remote", "power antenna", or "switched 12V". You will have to use the line outputs from the radio. If you use the speaker wires AND run it through the amp, you'll be amplifying the sound twice and it will be real loud and garbled when you adjust the volume just part way up.
Most newer cars added even more unnecessary complexity by using a digital data signal to turn the radio and amp on. For those radios you're just going to have to find the amp and bypass it. Sometimes you can find add-on boxes from places like Crutchfield.com that generate those computer signals, but they're usually expensive. It doesn't make sense to buy a radio to do away with the factory stuff, then spend more money to try to use what remains.
The original amps were used to tailor the sound to the shape of the vehicle. You don't need it if your radio will run speakers directly, as most aftermarket radios do. Bypassing the amp is a lot of work because you usually have to cut and splice 8 or more pairs of wires. You might ask at the dealer or places like Best Buy if they have a bypass plug. That makes the job simple.
Also, if there is no amp in the car, be aware there are always two power wires for digital radios. One is the switched 12 volts to turn it on and one is always live to maintain the clock and station preset memory. Some radios will be totally dead if that memory 12 volts is missing. Some will work fine but the clock will go back to 12:00 or 10:00 each time you turn it on. Some radios tune stations and read cds but have no sound when that memory line is not connected or the fuse is blown. Typically the clue is the clock and station presets reset to factory numbers each time you turn it on.
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