Grand Marquis 1988 Premium sound

Wondering if anyone has a current diagram for teh premium sound system in a 1988 Mercury Grand Marquis (4 plugs) and if they could give me an idea what is supposed to go where when installing an aftermarket stereo

Depending on which factory system is in the vehicle, you'll need one of these harnesses (look at the pics and compare to what the plugs at the back of your radio look like, then just pick the appropriate harness).  Also, I believe that not all of the plugs are going to be used with the harnesses, but again this depends on which system you currently have:

Metra 70-5005 or equivalent

Metra 70-5004 or equivalent

Metra 70-5002 or equivalent