WS420SQ - adding Bluetooth

I have a WS420SQ and just got the Wetsounds Bluetooth volume control. I am trying to hook it up. I only want it to come on when the rest of my system comes on. The Bluetooth only has a black and red wire. Which of those do I connect to the 420SQ? Red from BT to blue on 420SQ and black to black?

Thanks for any help!

depends how your blue trigger wire works. If you are just using your headunit's remote antenna lead to turn on your 420 with the blue wire, then you'd be putting an unnecessary strain on that circuit on your deck. If you have a relay between your headunit and your amps and 420 to turn them on, then adding the bt unit to that circuit is likely OK.

All that said, if you typically turn your battery switch to off at the end of the day, I'd just go to the red wire on the 420. That way, once you pair your phone with the bt unit, every time you power up the boat your phone will already be paired by the time you fire up the stereo. No lag waiting for the phone to pair with BT. And it's not like the power draw from the BT unit is significant at all either.

As long as the BT is on the boat side of the main battery switch,theres no harm in it being on even though the stereo may be turned off. However, a relay could be used to power up the BT when the amps turn on.