Hook Subwoofer up to House battery?
Considering possibly installing an aftermarket subwoofer (a modest, relatively low-power consumption one to enhance sound, not a ridiculous one to annoy the neighbors), but considering running it off of the house battery in order to avoid having to punch the 12V power line through the firewall. I'd probably want to terminate the power line in the 12V cigarette plug, and plug it into the receptacle behind the driver's seat. Of course the big potential problem here is draining the House battery dangerously low, so the trick is to figure out how to wire it so that this can't/won't happen. I imagine that the switch signal wire in the factory harness (the one that tells the amp if the key is in the "on" position) would tell the amp to stop drawing power when the key is off, but then the sub wouldn't work if you were running the radio with the radio switch in the "extra battery" position (and thus the key off). So this wouldn't really be the best solution since I'd want to use the sub when parked. Another idea would be to install a manual kill switch in the power line, but this would be subject to my memory function, which is poor at times.
Sorry if this is a dumb thread, but does anybody have any ideas? (How to do it? Why not to do it? I'm totally off base? etc.) Or - has anybody done something like this in the past and want to tell me how they did it and how it works?
Running a 2003 E-350. 12V electrical system only, no inverter. Isolator, not separator. Lifelife 4D battery.