I no longer own my 96, so I can help you with pictures or the like. But, the EVAP line is very easy to find. It is a sizeable (1/4" I think), line coming from the rear plenum/throttle body going towards the firewall. It is almost always one of the messiest lines that will leave your hands covered with black residue.
Follow it back. It will connected to the evap purge sensor and the solenoid. I do not remember the order. The solenoid is larger canister whereas the flow sensor is smaller.
From my own experience, diagnosing EVAP problems on this model year Mustang can be a PIA. Problems with the solenoid and flow sensor present in the same way. Both parts go bad in almost as frequently as the other.
The solenoid can be functionally tested. It should block flow with no power. Allow flow when power applied. So if this were my car, start 1st with a functional test of the solenoid.
Next, I would replace the flow sensor. It is not very expensive. It could save you a world of frustration starting with a known good sensor.
In my case, I made the mistake of getting replacement parts from a salvage yard. One of the replacement parts (the sensor) was bad as well. What killed me was the extream time it took to complete a driving cycle after any repair was made. I wasted TONS of time trying this and that.
When ever possible, get new sensors.