87-89 GT only.
There was a 4-light warning display that only came on those models. The pod contained a Low coolant, low oil, low fuel and washer fluid warning light.
ONLY 87-89 GT's have the washer fluid resevioir with a sensor. Pretty rare part so hard to replace. If the light it on, your best bet is to simply unplug it and just let it go.
Pull the driver's wheel and fender liner out to access the plug.