Behind the dash panel. Looking at the ST '03 wiring diagram, it looks like it's basically behind the fog light switch area. 2 GEM's one in front of the other. It looks like the one furthest to firewall.
It gets power from the fuse(drivers side panel)(key on)wh/bk wire, then through the relay(auxiliary box 1)(under hood,under intake tube, under
MAF sensor) then, TN/RD wire-grounded at the GEM itself and bk/wh wire to windshield washer pump motor. Then black wire grounded to body.(somewhere behind the coolant reservoir). Hope this helps