Wednesday, August 24, 2011

Mounting a TomTom GPS on a BMW K75S

There are few places to easily mount a GPS on this bike. But there is room above the dashboard switches if I could mount it below that. Turns out, the fork fairing is held on with 2 recessed screws. I removed the 2 screws and inserted 10mm long nylon spaces so that a mounting plate would be held off a short distance from the fairing and not rub.

I then made up a mounting bracket of aircraft grade aluminum so that I could attach an extension arm I had lying around. You can get similar things, including a cradle to hold the GPS, at

Aluminum Bracket with crinkle finish
Bulky GPS assembly
Assembly bolted into position
Side view of GPS mount (windshield removed)
Driver's perspective
You have to lift your head a bit to see the bottom of the dash, but it's the best compromise. There are thumbscrews on the mounting bracket to allow you to quickly remove the GPS cradle if you don't want it installed.

To test it, I used a PowerLet adapter with 5vdc converter and plugged into the port on the bike. But that wasn't an elegant solution with that rat's nest of wires. The better way is to build a power USB hub with built-in 12v DC to 5v DC converter. Couple options:
  1. Cyclenutz carries a weather-proof gadget with built-in voltage converter so that will make a clean installation and the same port can be used to charge a phone or other USB device. This is the easy solution. You could mount this right below the GPS or in the tray under the seat like in #2 below.
  2. Build your own. There is a simple way to do this; find an old converter that plugs into the cigarette lighter and gut the electronics. I then found a dual USB outlet and mounted everything in a $3 plastic components box you buy at Radio Shack. I connected it to a switched wire so it only runs when the key is on and an optional rocker switch in case I want to turn it off (the LED shows when it's ON). I ran one USB cable along the factory wiring to the handlebars. The 2nd USB port is available to plug in a cell phone and leave in under the seat when I ride.

5 volt DC power supply with 2 USB outlets

After all this work, I find that the GPS is virtually unreadable in sunlight. This is S. Florida (no tree canopy) so to see anything means I have to pull over and find some shade. Visibility is great in the evenings and that's when I seem to need it most. Or they sell a sun shade for $7 on FleaBay.


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