amp high level inputs?

Don't ever use those.....ever.

Just buy a LOC and step the high level down to line level and use the line level inputs.  But a decent quality LOC too, it shouldn't cost much more than $25. I'm no expert on brands or whatever, but I'm sure someone here can point you in the right direction. 

Why not tap into the speaker wiring behind the HU? probably easier than going into both doors.

Hmmm, I use those high level inputs all the time for factory systems. Very seldom do we have compatibility isses with the factory stereo. This jack is indeed the high level or speaker level input. The 4 pins are usuallt + - - + for the inputs. A quick check on the amp if it labelled or a check in the manual will verify this. If you do not have the molex that plugs in it, head into the local shops, they should have some kind of moles that will plug into it.

That said though, the outboard LOC is still a superior way to go. The better ones can take a much higher wattage input signal (not that you need it with most factory systems) and usually have a gain setting on them as well.  The scosche LOC80 is one of these. I too would go to behind the cd player to source my signal from, unless it is a factory amplied system, then I would source it at the amp.

http://peripheralelectronics.com/2002/loc.asp

this is a link to what u will need to do this install hope this helps

High Level Inputs are usually used when adding a Amp to a system with a Factory Deck, when no RCA outputs are available.

All you have to do is Tap into a speaker for the signal to the amp.

Be sure when you tap in to a speaker for a signal, to use a Mid range speaker NOT a tweeter as a tweeter will not have a full signal going into it and thus neither will your amp.

Hope this helps,

Dutch