Blower runs, no ignition. Diagnostic beacon is flashing 4 times, which according to to code sheet, means open limit switch. How do I remedy this?

Fan runs, but no ignition. Led flashhes 4 times, indicating open limit switch. Where is it, how do I fix it?

You probably have a least 3 switches in there. What is the model number? Are you talking about combustion blower or the big blower?