Edge 705 cadence sensor
 

How do you mount the cadence sensor from the Edge 705 on a tandem cranck? I have tried and signals in red and white are all right - the problem is that I can´t fully rotate the cranck without ripping the sensor of the cranckarm, because there isn´t enough space to the chain from the captain.
IbisTouche

Picture would be helpful.

Also throw away the Gamin magnet and use a rare earth magnet instead. See this article for an example: Tip: Improving Cyclocomputer Sensor Pickup

Are the chainrings on the inside or outside of the crank arm spiders? If they're on the outside, move them and see if that clears.

EDIT: Also, make sure your transfer chain is tight. A loose chain will actually move out to meet the magnet.