defog wire for 07 honda odyssey

This is the note that Audiovox has for the vehicle.  THIS VEHICLE USES DATA TO CARRY THE REAR DEFROST SIGNAL FROM THE A/C CONTROL UNIT TO THE UNDER HOOD FUSE/RELAY BOX, MUST USE RELAY AND FUSE AT 30 AMPS

This is the info thay have on the wiring.

Rear Defrost

BLACK / YELLOW

\They do not list a location for the wire.  I can only assume that you need to catch it under the OEM relay at the under hood relay/fuse box.

Thanks... what do you mean by the vehicle uses data to carry the rear defrost signal? I cant just trigger it with a relay using + / -

They mean that you can not use the wires at the actual defrost switch mounted on or near the ac control unit.  That switch sends a data signal to the AC control unit that in turn triggers the under hood relay.  I have no idea if you will have problems if you just try to trigger the coil of that reay to get it to come on.  I do know that if you use a second relay to apply power to the wire they have listed, there is no way to damage the AC control unit.  That wire is isolated from the AC control unit.  Groinding or powering the appropriate wire of the coil of the OEM relay could cause problems.  Unlikely, but if it were me, the second relay would be the way to go.