I believe that model has a two or 3 piece radio system. On the passenger side trunk behind the liner is some of the radio system. It is a tuner and /or two amplifier system. Hold your hand on these components to see which one might still be warm after your car sets. If warm, you have found the drain. You can also unplug the power wire or on in unit fuses to see what happens. Sometimes the power to the antenna sticks on so you must unplug the power from the unit on the power antenna. The amplifier box stuck on on mine which was a 124 model. You should also use a digital voltmeter to look for the drain by testing the battery voltage after you have disconnected something and waited a while because digital is more sensitive. Chances are its a rear trunk ampliflier.