I read the 667 manual and realize you don't need a 3rd hand to intiate the trigger. If I read it right you can set it to high (see P.93) in manual mode and it should give you the 12V d.c. until you set it to low. If your voltmeter does not register 12V then either something is wrong with the 667 or the cable/plug. If it does show 12V then you need to start troubleshooting the PureAV. Does the PureAV specify any current requirement. The 667 trigger out is rated 0.1A, that is 100 mA, hopefully the PureAV does not require any more than that, it really shouldn't but I am not 100% sure.