Be aware that the OVMS module (at least the V3) appears to use more pins that most of the common engine monitoring dongles. Many extensions and Y cables don't work correctly -- there may be some telemetry, but some information and capabilites available with a direct connection won't work. The reason is that many cables only connect some of the pins.
It took me 3 tries (although I admittedly may have had better luck if I didn't go for the cheapest available... :) ) to get a cable that worked. The first one I didn't know there would be a problem, and the second one (despite being labeled a 16 conductor, straight through cable) was missing some connections. But persistence paid off, and I now have a functional module, where I want it, and with enough slack to be able to easily shift it around, if required.
If you're looking for an ODB2 extension, be careful what you select. :)