best place to to tap LOC and 12v trigger? unless there are any harness adapters or something you can buy which avoid having to tap wires.

 

There are a couple harnesses that you can get off eBay that will let you use the factory radio harness without having to splice in to anything. Not the prettiest but better than wire taps, IMO.
http://www.ebay.com/itm/Add-An-Amp-A...NSS4rv&vxp=mtr
http://www.ebay.com/itm/Amplifier-Am...iMizWA&vxp=mtr

Otherwise you can just tap the harness at the back of the HU and run RCAs and a power lead from an LOC with amp trigger from there.

 

Thanks, i will check those out.