Connecting the Becker Line out module to a modern amplifier

I’m currently planning to install period correct Becker radios into my 450SLC and 560SEC.   I previously outlined the radios I plan to use, and tested them.   I was able to confirm that the Becker 1402 destined for my 560SEC was working correctly.     Rather than using the internal 2x25W amplifier in the Becker, I planned to connect it to an external amp.   While I could have used speaker level inputs, I was hoping to leverage the Becker Line out module to connect to the amp using normal RCA inputs.

Becker Line out module

The Becker Line out module was part of the Premium sound option in the series 2 W126 cars.   For some inexplicable reason, it was not offered in Australia.   While there was a version of it for the 86-88 cars, it really came into its own after the interior facelift.  These cars had additional door speakers as well as the factory amplifiers.   In any case, the internal amp powered the front speakers and the Becker line out module connected to the twin amplifiers behind the rear seat.   One for the left speakers (rear deck and door) and one for the right.  In many ways the Premium sound option was the main thing that made the facelift worth doing.

While I wasn’t 100% sure the Becker line out module would work with the 1402, I felt pretty confident.  I could see the plug for it on the back of the radio, I and I had seen it offered on some of its sister radios such as the 780, 1480 and 1432.   I sourced mine from the USA, where the premium sound package was quite common.   The part number is 001 820 63 89.

Becker Line out module

The Becker line out module has its own proprietary plug, but the three pins were pretty obviously a positive wire for the left and right channel and a shared negative wire.   That should be sufficient to connect to RCA connectors.   I ordered a pack of female connectors that ended in bare wires to make it even easier.

Not sure of the significance of the wire colours in the Becker harness, but I found that the red Becker wire connected to the white RCA wire,  blue to red and both white and yellow to black.   The centre pin needed to have two wires in the Becker setup as there were two separate amplifiers.    For this project I thought I would try those connectors that use a heat gun to melt the solder.   Seemed to work quite well.   I stupidly forgot to put the shrink wrap on the wire before I joined them up, so once done couldn’t get it over the plugs.   Just used electrical tape in the end.

Installing the Becker line out module was a simple matter of just plugging it in, and a small Philips head screw.    To test it, I grabbed my powered computer speakers that accept RCA inputs.  I had left my test setup intact from a few weeks ago.  That meant it was a simple matter of unplugging the regular speakers and substituting the RCA connection to the computer speakers.

Becker Line out module

The test worked great.   As you would expect the volume was quite low, even though the PC speakers are powered.  That is fine as the amplifier accepts low level inputs.

To complete the installation, I have gone with an Alpine KTP-445U.  This is a very small class D amplifier that should meet my needs.    There is a good write up of its capabilities here.   I’m not looking for doof doof sound.   I just want a decent four channel amplifier so I don’t have to run four speakers off 2x25W.    The Alpine unit is really small to fit into the Mercedes dash (it’s as long as my hand).  It also has a number of useful features that I will use.   It can convert two channel input to four channel output and has built-in high pass crossovers.   This is useful given the comparatively small size of the speakers that fit into a W126.  I was also only $175+GST.  I will probably use the antenna signal to trigger the amplifier on/off.


As I write this, I have been listening to music from my phone (via the bluetooth FM injector) going through the Becker 1402 and line out module and it sounds great.

Becker Line out module

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