How to install a 2 port USB power adapter in an ‘87 BMW

For some reason BMW forgot to put USB power sockets in my ’87 535is.

In addition, while the JVC stereo the previous owner installed has a USB port, I use it for a memory card for music. Lastly, the cig lighter socket in these cars is “always on”.

For these reasons I decided to do a little mod: Adding a 2 port USB power socket. This post explains how I did it and the parts I used.

Here’s the final result:

To start, I went to Amazon.com and bought 4 different cigarette lighter USB power adapters. I wanted to find one that had two plugs, supported Apple’s proprietary USB charging protocol, and would fit well behind one of the blank plates BMW provided on either side of the radio. Amazon’s amazing return policy meant that, as long as I didn’t damage them, I could return the ones I didn’t use.

After carefully pulling all 4 apart, I found that the PowerGen Dual USB 3.1A 15w High Output Car Charger had the following favorable characteristics:

• Up to 3.1A output.
• Red LED.
• A short circuit board. Some of the others had boards that were almost 2 inches long.
• A USB plug design that would adapt easily to a different bezel (in this case the BMW blank dash plate).

Disassembly of the power adapter was simple: just pry the plastic apart and the innards pop out.

See how the USB connectors hang over the edge of the circuit board? Turns out they extend almost exactly the same as the thickness of the blank plate!  (The blank plate in this picture is a spare that has a hole dilled in it for an alarm LED).

To cut the right sized rectangular holes in the blank plate I needed to use the faceplate from the USB adapter as a template. The USB connectors already fit the original faceplate tightly, but I wanted to make sure the new holes were very-slightly undersized to create an even better mechanical connection.

I used a pair of small Vise-Grips to hold the faceplate in place on the back side of the blank plate (I had to cut the sides of the original faceplate a bit to make it fit) and then drilled a pilot hole in the center of each rectangular opening. I then used a very small flat file to carefully expand the pilot hole and create the new rectangular holes in the blank plate.

I de-soldered the old ground wire and positive wire (spring in the above picture) from the circuit board and soldered in new wires of appropriate length. I then used a hot glue gun to further secure the electronics to the blank plate.

Remember, because I made the holes slightly undersized (10ths of a mm) the USB connectors fit really tightly providing a good mechanical connection.

From here it was a simple matter of attaching some plug connectors to the wires on my adapter and their siblings in the dash (which I had previously exposed behind the right hand side plate when installing my Valentine One radar detector hard-mount). I plugged it in and snapped the plate into place.

I have it wired to the same circuit as the radio so that it is only on when the ignition is on. You’ll note that the red LED does a nice job of providing a little illumination of the sockets (that matches BMW’s instrument colors). The hot glue helps diffuse the light a little which is a nice touch.

Hope this helps others.

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