Have a Trane XE90 furnace, when turning on heat this year for the first time the furnace blows an inline fuse that is on the output of the 24v transformer. Had a similar problem in the past that turned out to be the thermostat that is why it is now fused. Disconnected all wires from thermostat to furnace and to AC unit, then jumpered the red to white posts on the control board to turn on heat and still blows the fuse so it does not appear to be external to the thermostat or AC unit. Having difficulty reading schematic as it is very old, Does the 24V feed the sensors on the furnace such as the pressure switch? flame sensor? gas valve?, Could these be part of it. Where else does the 24V power go to that could cause a short. Are there other wires on the control board that could be removed 1 at a time to find the short? Looking for any suggestions.