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2005 c230 kompressor
6 Posts
Discussion Starter · #1 ·
hello, I am in the process of installing a head unit and subs in my 2005 c230k non-bose sedan. Among many other questions, where should the remote turn on wire for the amp go? is there any reason to not hook it up to switched ignition power that runs the head unit itself?

8 Posts
Blue Wires Explained

Not all aftermarket radio installations require you to connect the BLUE or BLUE/WHITE wire to anything.

Definitely do NOT connect it to a switched ignition source. This is a low-current (but still 12 volts) wire, meant for turning on an external amp or power antenna.

There are really only (4) wires you need to connect, other than speaker wires.
From the aftermarket radio:
Black = Ground
Red = Switched 12 volts
Yellow = Constant 12 volts
Blue or Blue/White = Amp turn-on or power antenna

If you are not installing an outboard amp, then all you need to figure out is whether or not your car has an FM antenna signal amplifier, which is a small shiny steel box in the back somewhere. Don't bother looking for it, just test the wires coming out of the back of the original radio with a Power Probe III or a meter.

See if there is a wire which becomes 12 volts when the radio is ON. If so, it most likely is turning on the FM antenna amp.

Another way to test this is to hook up just the black, red and yellow wires from the new radio, and the FM antenna cable. Tune manually to 87.5 FM then press SEEK UP. Write down how many clearly listenable FM stations you are pulling in, from 87.5 MHz FM up to 108 MHz FM.

Compare this number to how many stations the old radio pulled in. If they are within 10 of 15% or each other, then more than likely you can just skip trying to find a use for your BLUE or BLUE/WHITE wires. in other words, your car probably does NOT have a powered FM antenna signal amp.

If you are not getting enough FM stations then yes, you need to use the BLUE or BLUE/WHITE wire to power up the FM antenna signal amp.

Note: The reason for (2) blue wires is that in the old days, cars had power antennas that went up and down when you were listening to the tuner. When you turned off the radio or went to cassette tape, now CD, the antenna would go down. This was so that you could drive through a car wash or low-clearance garage with your power antenna down. Read the installation instructions for the new radio - it calls out which blue wire does what. You will need one of them to turn on your outboard SUB amp. In the car stereo world, this is referred to as an "amp trigger wire".

The circuit designers gave some thought to this - the idea was to reduce the number of UP/DOWN cycles of the power antenna motor, yet still have it retract into the fender when needed. Nowadays, it just confuses people.

One of the BLUE wires is an amp turn-on lead which stays on with the radio. The other BLUE wire turns ON/OFF depending on whether or not you are listening to the radio, i.e., AM or FM.

The German carmakers started using this wire to power up an FM antenna signal amp, which of course turns ON and OFF with the radio. Call me if you need help: 603-682-5888
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