TSB 93-26-01
http://www.bbbind.com/free-tsb/
'85-94 Bronco (IDK why that's not '85-96)

ISSUE:
An inoperative electric rear window defroster (heated backlite) may be caused by bond separation of the pigtail terminal to bus bar or broken grid lines.

Heated Back Window Grid Wire Test

* Using a strong light inside vehicle, visually inspect wire grid from outside. A broken grid wire will appear as a brown spot.

* Run engine at idle. Set the heated back window switch and light (18C621) to ON. The indicator lamp should come on.

* Working inside vehicle with a Digital Volt-Ohmmeter, contact broad (bus bars) red-brown strips on sides of rear window. The meter should read 10-13 volts. A lower voltage reading indicates a loose ground wire (pigtail) connection at grounded side of glass.

* Contact a good ground point with negative lead of meter. The voltage reading should not change.

* With negative lead of the meter grounded, touch each grid line of heated back window at its midpoint with positive lead. A reading of approximately 6 volts indicates that the line is good. A reading of zero volts indicates that the line is broken between midpoint and the positive side of the grid line. A reading of 12 volts indicates that the circuit is broken between midpoint of grid line and ground.

Owner caption January 2007 · Photo 1409 of 5000