I just pulled the manual for the P20 HD tuner down from Crutchfield and was reading it. It says the power wire should be connected to constant, not switched, power. However, the manual for the Z120 says that you shouldn't tap anything off of the constant (yellow) power supply line. So just where should the HD power lead be attached? Ignore what the headunit manual says and tap into the yellow line? Ignore what the HD tuner manual says and attach it to switched power like my unused power antenna line? Or is there a third option that I'm not even considering? How did you all do it?

I just pulled the manual for the P20 HD tuner down from Crutchfield and was reading it. It says the power wire should be connected to constant, not switched, power. However, the manual for the Z120 says that you shouldn't tap anything off of the constant (yellow) power supply line. So just where should the HD power lead be attached? Ignore what the headunit manual says and tap into the yellow line? Ignore what the HD tuner manual says and attach it to switched power like my unused power antenna line? Or is there a third option that I'm not even considering? How did you all do it?

I would think that the gauge of the yellow wire was sized to handle the rated HU max 10 Amps. So adding additional accessories tapped into it could overload it. I don't know what the P20 draws. Best to either tap off a different constant +12V circuit or run a dedicated (fused) wire from the battery. Since the manual specified constant, hooking it to a switched will likely reset the tuner - wiping out various static data. This would probably have some adverse affets on operability - but it would likely still operate. Don't use the antenna power - it is only rated enough to trigger a relay (max 300mA).

I would think that the gauge of the yellow wire was sized to handle the rated HU max 10 Amps. So adding additional accessories tapped into it could overload it. I don't know what the P20 draws. Best to either tap off a different constant +12V circuit or run a dedicated (fused) wire from the battery. Since the manual specified constant, hooking it to a switched will likely reset the tuner - wiping out various static data. This would probably have some adverse affets on operability - but it would likely still operate. Don't use the antenna power - it is only rated enough to trigger a relay (max 300mA).

I thought some more about the antenna as soon as I posted and thought that would be a bad idea. But I hadn't contemplated why there would be the need for constant power. You're right. If I hooked it up to switched power, I'd most likely lose my presets every time I cycled power. I really didn't want to run a line from the battery, but if that's what I have to do, then that's what I have to do. Thank you for the comments!