I had a similar problem with a 3200GTA. There is some similarity between the cars so my comments may be relevant.
My problem turned out to be due to the air con which has a condensation collection tank somewhere behind the dashboard and out of site. This tank has an outlet which is a rubberlike tube that passes excess water to the exterior by descending through the floor. It has a slightly fish tailed end (if I remember correctly) and it had become clogged with dirt and gunge from the road. Cleaning this (from underneath the car) allowed the water to escape properly. Otherwise it just overflowed onto the left hand side passenger footwell especially when I turned the car briskly to the left. In the 3200GT this created another problem given that the fuse board was mounted below the passenger footwell and didn’t like getting wet. Needless to say the problem fist showed itself when my wife was wearing a brand new pair of light coloured shoes!
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