Locating the W126 X30 power block on RHD cars

I’m currently planning to re-install the Becker Radio in my 1987 560SEC.  At the same time I will be installing a small amplifier, a bluetooth FM Injector and a couple of unobtrusive USB charging ports.

The second generation W126 wiring harness provides a factory way of adding additional accessories.   This is the X30 power block.   Up to 8 accessories can be connected using factory plugs and their own wiring harnesses.   The number already connected will depend on options installed on the car.

Other than the direct power for the amplifier, I plan on using the X30 power block for the rest of the accessories.     The x30 power block provides five pins, each with a specific purpose.

1. Hot at all times:   Power from fuse 15 (8 Amp)
2. Hot in run or start:  Power from fuse 8 (16 Amp)
3. Ground
4. Illumination.   This is for accessories that have a small bulb activated with the headlights
5. Hot in accessory, run or start:  Power from fuse 19 (16 Amp)

This provides pretty much all the options required when installing a standard accessory.   Obviously something that draws decent amperage will need a direct connection from the battery.   These fuses are shared with other features.

For the amplifier, I’ll probably just use the ground.   I’ll take constant power directly from the battery as it requires up to 15 amps.    For the USB ports, I’ll want to use pin 5 and pin 3.    For the FM injector, I’ll trigger it from the radio, but use pin 5 for its actual power source.    I shouldn’t need pin four, unless I can’t locate the standard illumination wire for the Becker radio.

The electrical manuals I have for the W126 are for the USA versions.   The core manuals do a fairly good job of covering other models too, but the electrical manual is quite US specific.   According to that manual, the X30 power block is available in the diesels, 420SEL and both 560 models between 1986-1987.   For 1988 it was only installed in cars that had heated seats.    In those years many standard accessories were now hard wired in.

This explains why the 1988 560SEL I grabbed two X30 harnesses from only had the two.  One for the front heated seats and one for the rear.  Earlier cars would have had more.

Since the 300SE/SEL models were not offered in the USA until 1988, I am not sure if the 86-87 models were standard with the X30 power block.  In any case my 560SEC is an 1987 and has heated seats, so the X30 power block should be installed.    I guess it was cost cutting that removed it for later years.

My other complication was that I didn’t know where the X30 power block was located on right hand drive cars.  On left hand drive cars, its under the dead pedal in the drivers footwell.   This location is specifically referenced in the manual.

Luckily I had my 420SEL parts car to use as a guinea pig to search for the X30 power block.   As a 1987 model it should have one.   The first place I looked was under the dead pedal.   I figured if it was in the same place for RHD and LHD cars the manual would have said it was on the left hand side of the left hand footwell.    It wasn’t.

Next place I looked was where the dead pedal would be if my car was LHD.  I had to remove the under dash panel, the bonnet release catch and the trim piece under it.   It was worthwhile using the 420SEL as a test, as I broke the plastic retaining clip trying to remove it on the 420SEL.   That gave me an opportunity to examine it further to ensure my removal didn’t break it on the 560.

Sure enough, the X30 power block was in pretty much the same spot on LHD and RHD cars.   Its an ideal location as it’s right next to the conduit going to the rear of the car.    Not only was it there on my 420SEL, but three accessories were present.   The cover was also still there and not broken.   Great to have as a spare.   The photo above shows the X30 power block with the trim removed on my 420SEL.  It’s the tall rectangular thing in the centre of the photo.    The photo below shows the cover off and how the accessories connect.

That gave me the confidence to locate the X30 power block on my 560SEC where even more accessories were plugged in.    I also found a rats nest of old wires for the previously removed car alarm.   I plan to clean this up as part of this installation.

The X30 power block provides an easy way to install additional accessories on your W126 should it be present.  I understand it is also present on some W124s as well.  It means no alterations to the factory wiring harness are required.