W116 Hidden bluetooth box

My 450SE is still equipped with its original Becker Mexico Cassette 485.   The Becker works beautify including the wunderbar.   For Australian delivered cars, the Mexico Cassette 485 was only for 1978 model cars.   The main visual difference between the 485 and the other pinstripe Beckers is the model script, which is all caps BECKER MEXICO.

Naturally I wanted to keep the radio in the car, but be able to play music through my phone.  The Becker Mexico does not have a line in capability, so I used the iSimple Tranzit Blu HF.  This is the same as on my 450SLC and other cars.   This unit is essentially a box the size of a deck of cards.   It plus into the antenna source of the radio, transmitting an FM signal onto the antenna wire, rather than into the air.  This provides a much cleaner signal than most FM transmitters.   The regular antenna plugs into the unit, so when it is disabled, regular radio reception is possible.   There is a small control button and a microphone for bluetooth calling.

I’m glad I bought a few of these units a few years ago when they were on sale, as they no longer seem readily available.   From what I gather, there are three variants, the ISFM23, ISFM2351 and the ISFM2381.    The first two seem discontinued, and the latter is always listed as out of stock.   This is a shame, as its a great solution for classic cars.

As with the other cars, I also put in a couple of USB charge ports so I could charge my phone and not leave the ashtray hanging open.

I didn’t want to modify the car in any way, so I simply unplugged the power feed to the cigarette lighter and used it for the Tranzit Blu and the USB charging ports.  Luckily I even had a section of MB wiring harness from a W126 washer bottle pump that plugged right in, thanks to my old 420SEL parts car.

I wired it up so the USB charge ports were on switched power like the cigarette lighter would have been.   The Tranzit Blu is wired in the same way, but a relay only powers it on when the Becker is switched on.  I did this by using the antenna trigger to enable the relay.   The relay then powers the Tranzit Blu and also trigger the antenna.  I’ll probably add a hidden switch to control the antenna.  I often park under a hoist which would damage the mast if I forget to switch off the radio.

This job was a little harder on the W116 than on the W123 or W126.  When the ashtray is removed, There is a backing plate that prevents access to behind the radio.   The job is still quite straightforward, but a little fiddly.

I built the wiring harnesses I needed outside the car, and then proceeded to remove the Becker.  The Becker radios have their own mounting system based on mounting hardware that is tightened by a large flat head screwdriver.    I also had to remove the carpet section under the glove box to get access to the Becker amplifier (for the antenna trigger) as well as under the steering wheel to mount the control button on the underside of the steering column.

Testing everything without putting it all back together properly revealed some strange behavior I could not work out.   I was only after I got my power probe out that I realized my mistake.  I had assumed that since the brown wire went into one side of the plug, it was the ground.  The wires were probably crossed inside the plug.   Not only did that cost me an hour of time, but I shorted out my Tranzit Blu.   That was really frustrating since these are now hard to get.   I had one more that was earmarked for the 560SEL that I had to use.

Once I sorted out my mistake, the rest of the installation went fairly smoothly.  I was able to get the Becker back in and correctly in the dash.  I also installed a missing plastic retainer for the glove box insert which is the same as on the W126, another part from my parts car.

The install was in time for the drive down to Canberra for the ACT German Car show. Having bluetooth audio through my Becker made the drive much better.