Had a Trane XL90 two-stage high efficiency gas furnace installed in 02'. Open limit switch diagnostic L.E.D. came on last night and the electrical schematic is completely corroded need help finding the switches. Thermostat said 43 this morning.

Sorry but no diagram here. You usually can locate the limit switch buy description. Usually the size of a quarter with 2 or more wires on it.

Usually they are held in place by two 1/4 inch screws.

Look at the sticky notes at the beginning of this board for some pictures of limit switches.

The manual reset switch on a Trane XL90 is mounted upside-down ON THE BOTTOM the silver burner box at the top of the furnace (the silver box with the window that encloses the burners). The little red switch itself is obscured by the two leads that connect to it, but if you look from one side, you'll see the small red switch -- push it once and you're reset.