I got a goodman GMT090 and I would not ignite. So, I cleaned around the burners, sandpapered the sensor, check that the ingitor was intact. I than noticed that the motherboard light was flashing 4 times. This is supposed to indicate that the main limit switches were an issue. So upon a little internet research, I took the wires and limits to a heating store. They checked them and said that all were properly working. But, suggested that it may be other limits above or below these. I didn't see anymore. But, I did see an orange wire that was connected to the sensor on one end. I attempted to bypass this limit to check. Now, furnace motor or anything will kick off. Just the motherboard confirming electricity will blink once. Any advice. I think I getting to whits end with this. I no advice, it'll be time to call the pros.