what is the difference between (3) Map sensor or circuit electrical fault, and (5) Map sensor mechanical fault? ( btw this is for a 89 civic hb si 1.6L ) ecu code read outs,

 

Trouble Code descriptions taken from Alldata Workshop manuals:

DTC #3 - Most likely an electrical problem in the Manifold Absolute Pressure (MAP) sensor system
Problems such as a electrical issue with a poor or intermittent electrical connection, workshop manual says to check the electrical wiring to the map sensor first when this code comes up.

DTC #5 - Most likely a mechanical problem (broken hose) in the Manifold Absolute Pressure (MAP) Sensor system.
Problems such as a vacuum leak at a hose or manifold, check manifold vacuum and map sensor's ability to hold vacuum. You could also component test the map sensor and see if it puts out the corresponding voltage at the proper vacuum ranges. See chart below:

125mm Hg (5in. Hg) ................ 2.5 Volts
250mm Hg (10in. Hg) ............... 2.0 Volts
375mm Hg (15in. Hg) ............... 1.5 Volts
500mm Hg (20in. Hg) ............... 1.0 Volts
625mm Hg (25in. Hg) ............... 0.5 Volts