Using the USB data lines

[futekmek]

I've built a device that uses a Digi Pro and the speed sensor pulse in my car. I want to power the Digi using one of these, which I would hide under the dash:

http://www.ebay.com/itm/KIS3R33S-5V-USB-DC-7V-24V-to-5V-3A-Step-Down-Buck-Module-For-Phone-MP3-MP4-PSP-/321568958040?ssPageName=ADME:L:OC:US:3160

I also have to run a wire from the speed sensor to the Digi Pro, but I'd rather not have an extra wire (other than the USB cable) going into my device enclosure. If I'm powering the Pro using USB, are the data lines in the USB cable being used? Can I use one of the data lines as my speed sensor pulse wire? I would run a wire from the vehicle's speed sensor and solder it to the USB data line on the power supply above, then run a jumper from the Pro's USB data line to a digital pin on the Pro. Is this possible or just stupid?

[digistump]

As long as that module isn't putting any voltage onto the USB data pins (some do to tell the iphone at what rate to charge) then you can use the USB data lines - just be aware that pin 4 has a 1.5k pull-up on it - so using pin 3 would be best.