#tranzitblu

My 1981 240D was sold new with a Becker Europa 596 Cassette. The Becker was still in the car when I purchased it, but it would not stay tuned. It would randomly drift out of tune and need constant adjustment.   I found that rather annoying, I removed it to be serviced and put in a Europa II temporarily.  A friend in the Mercedes club was able to help me get the radio serviced.  It is now working well. I got the radio back last year, and finally found time to re-install it.    I had also seen on Instagram where anther W123 owner had installed a USB charge port meant for an E36 BMW in place of the factory fader.    My factory fader is still working, but my 240D has two switch blanks on the top console, which is the perfect spot for a charge port.   The USB charge port was quite expensive, but it looked like a really good solution so I ordered one. To power the Becker 596, I also planned to install another Tranzit BLU Bluetooth Box.   This is the same solution I have used in my 560SEC, 300TE and 450SLC.   I'm very happy with it.   The Tranzit BLU is a small box, about the size of a deck of playing cards that provides a FM signal directly on the antenna wire.   This makes it far less susceptible to interference.  It also provides a handsfree option for calls.

Normally the Tranzit BLU is controlled by a hidden button.  However, I had the idea of using a factory sunroof switch in the other blank switch location instead.   I didn't have a W123 sunroof switch in my box of parts, but I had one for a W116 or W107, which is good enough to test with. The installation was pretty simple.  I use the connector for the cigarette lighter to power the USB charge port.   The spade connectors that came with the charge port were too narrow, and not quite long enough so I made some extensions.   In testing the USB charge port, I was also able to easily pull off one of its connectors, so I crimped on a new one. Since the USB charge port is designed to be added to an E36 BMW, it has been designed to piggy back off another accessory.   Therefore, it already had power and ground connectors for the Tranzit BLU.   I used a relay to trigger the Tranzit BLU from the Becker Antenna trigger.   That relay then powers the Tranzit BLU and also triggers the power antenna. Instead of the button that comes with the Tranzit BLU, I wired in the sunroof switch.  I used a multimeter to work out which of the four pins are activated when the switch is pressed forward.   Essentially the way the switch works, is when it is pressed, it joins power to one side of the motor, and ground to the other side.   Thus, pressing the switch the other way reverses these connections, allowing the motor to run in reverse.   I assumed for this purpose I just needed to make the connection to trigger the Tranzit BLU.  Turns out I was wrong.

I wired it all up and did a quick test of the system.   I was able to pair my phone and play music through the Becker 596.  However, the switch did not work.   I tried a few more pin options to no avail.   I had assumed that the switch was 'dumb' and just made a connection to trigger a press of the button.  However, it was looking like that was not the case.   I got the Tranzit BLU switch and connected that to a multimeter.   On very high resistance settings, I was able to trigger a change in resistance when pressing the button, but it wasn't constant.    Given there appeared to be more to this button than I anticipated, I gave up and put the switch blank back in place.    The Tranzit BLU button is now on the steering column out of sight like in my other cars.

Despite the failure of using the sunroof switch to power the Tranzit BLU, I am very happy with the setup.   The correct Becker is back where it should be and I can play music through my phone and make and receive phone calls.    I am taking the 240D on its first road trip this weekend, so having music will be great.   The install is totally reversible with no factory wires cut.