The hatch receiver is what locks down the rear hatch when closed. It comprises a white plastic plunger which will push up the hatch slightly when its released and switch on the car interior lights. It seems that the interior light circuit is often the culprit for battery drain. The GTS owner in this thread took the car away before I could complete tracing the problem, but I found a possible cause with the overhead lamp assembly near the sunroof.

 

The hatch receiver is the piece where the hatch lock enters. The interior light switch for the hatch opening is at the bottom of the receiver. Take the tool panel off to check it. The wires to the switch are normally brown (ground or earth) and brown/white (switch ground or switched earth).

There should be continuity thru the switch (checked from brown to brown/white) when the hatch is open, no continuity when the hatch is closed.

 

I know this topic is flogged to death, but I found my battery drain problem ('92 ROW GTS, ex-Japan) in the radiator shutter-stat controller - which the PO had left installed and connected when he/she removed the radiator shutters and their underhood positioning system. Disconnected the controller and voila! Drain dropped from .7 Amps +/- to 20-25 mA. Other posters have said - remove and/or disconnect all inoperative equipment, and all accessories added by the PO as a first step Thank you to the listers who pointed this strategy out. Much appreciated...

 

Had a similar drain on my 90 GT. The glove box was not closing far enough to switch the light off.

Also had a drain on my 94 GTS. The stock amp was drawing current with car off.