If you have a stock amplifier or pwr antenna, you can tap that lead.
The stock HU should be able to support two trigger feeds; aftermarkets can support 3, IIRC.


Tapping the lighter will turn the amplifier on all of the time as opposed to turning on/off with the headunit.
There's not really much of a problem unless you have a situation such as jumpstarting, testing your battery & alternator, etc.

 

I plan on wiring a master switch so I can have the radio with no sub.

 

If you're wiring in a switch for the remote lead, then tap whichever is convenient.

 

I like it, Stocker! I did the same kind of thing - a switch on the remote wire - controls the sub amp only ( I have 2 amps) for talk radio/AM listening.

Comes in handy - I hate having the traffic reports THUMP in my head