I have to admit, I find it more than a ltitle bit frustrating that I have to rely on google searches to find photos from various websites and forum posts to try to discover the actual wiring for the Paris boards, and with the release of v4.0, multiwii.com have removed all mention of the v3.0 boards from their site(?!).
I have a Paris V3 and I will admit that formal documentation was sparse (just a few example photos are all I ever found). But now that they have removed all V3 material from their site I can see how it would be a whole new level of frustration.
Back On Topic... still no luck at my end. I've gone over the board with a magnifying glass and multimeter, no shorts/brigdes anywhere, and it is a brand-new WM+, so surely I can rule out a faulty board?
For now, let's assume your WMP is ok and you don't have any wiring issues. If you closely follow these ten steps I expect you will have better success with your TriCopter:
1. Download MWC V1.9 again. Yes, download it again. Verify it has the Nov-12-2011 date stamp. Use this file set in place of what you have now, even if it appears to be the same.
2. Edit the V1.9 config.h and enable TRI (uncomment #define TRI). Do NOT enabled the internal pullups. Avoid any other edits for now (you can re-edit config.h after the WMP sensor is working).
3. Verify that your Arduino Pro Mini 328 is the 5V version and not the identical looking 3.3V CPU. Do this by measuring the voltage on the Arduino's Vcc pin. If 5.0V, you are good to go. If 3.3V, then I recommend you get the 5V CPU version.
4. On the Paris V3 board, disable the 2.2K pullup option on the bottom of the shield (remove solder from the solder bridge pads). Do not use these pullups!
5. Wire the WMP as before, but for the new V1.9 firmware please connect the WMP's Vcc power pad to 5.0V instead of 4.5V (D12) or 3.3V.
6. Add external 2.2K pullup resistors to SDA and SCL. The resistors must be sourced with 5.0V (not 3.3V!).
7. Power it all up and verify that the WMP has 5.0VDC at its power/gnd pads (measure at the WMP board, not elsewhere).
8. Launch the GUI and press start. Verify that the R/C controls are working by watching the GUI.
9. Watch the Debug2 status window. If the value is greater than zero then your sensor is bad, wiring is wrong, or some other hardware issue needs attention.
10. If Debug2 remains zero and your gyro data changes as you move the model, then pop the cork on the bubbly. Otherwise, report the debug2 value and all symptoms. Plus post some new photos that may help us see what you've wired up.