Re: Where are EEC-IV connectors in'91 TBird
US-built Fords around this era have two connectors on the harness running down the driver-side inner fender near the brake booster. One will be a square connector with a single wire (Self-Test Input) and the second connector is a trapezoidal shape with five wires (Signal Return, Data Positive, Data Negative, Self Test Output and Fuel Pump Relay). Sorry, can't tell you the colour codes, as the book I have doesn't list them, just what they are - really helpful! But you should have no problems finding them.
Sunpro makes a great little Code Scanner for EECIV cars - part number CP9015. I bought one about 10 years ago when I was in the US - cost about $25 from memory. Comes with a manual explaining use and all fault codes.
BA GT #0909 - Manual, Citric Acid, Stripes, Sunroof, Premium sound, FPV Steering wheel and Mats.