I have a Trane XL80 (Model #TUD060A936A0) that has been converted to a White-Rodgers (Model #50E47-060). When the thermostat calls for heat, the furnace short cycles until it is manually shut off. There is no indicator light on this unit to tell me what the problem may be.

What else could make this furnace short cyle besides this box? Any suggestions on how to repair?