Good LOC’s?

I differ on some of kirk's opinions here.  It's not the LOC itself so much as the fact that with a factory deck you have to use the high level output.  The signal is "dirtier" than a low level signal.  The voltage is higher but the signal is smaller.  One thing you'll note right away is that when you are finding the clipping point on the deck it will invariably be at about the halfway point.  (Low level signals from aftermarket decks start clipping much farther along on the volume dial.)  Setting the amp gain to that halfway point results in a smaller control sweep when you're adjusting volume.

I use LOCs in my personal car because of several reasons:  the expense of the dash kit (Taurus) and having to get rid of a good and trouble-free Clarion factory disk changer being two of them.  The overall sound is very good, but I spent a considerable amount of time and effort getting the LOC's set just right.  I twisted the LOC input wires, as well, to keep out induced noise in the wire runs from the factory wiring.

The other is the quality of LOC you should seek if you are set in keeping the factory radio.  Use only those rated as "high quality", which will start in the $20s.  It will have gain adjustments and other higher quality attributes that will enable you to get the sound quality as high as it can be.  It takes some effort;  you usually can't get best results by sticking in a $10 converter and calling it a day.

But the Audio Control device forbidden spoke of is the best way to go.