AllData, MOD/ShopKey, Identifix, the factory service manual for the vehicle in question, or (and last in the list for a reason) a generic Haynes/Chilton repair manual for said vehicle.
If you're lucky, check with some forums that deal specifically with your model vehicle and you might be able to find the information you need.
Though if you were just a bit less generic with your question, maybe you could just get some help here. The minor things like make/model/year/engine/trans and what exactly it is that you're looking for.
Yes it is for radio/gps unit. So far I have not found a location or color of wire on on any web sites. It not needed if you do not lose the gps signal. So it not to import but I would like to be connected any way. -- Caddy