Limit switch open?

[2004 Lennox Merrit series gas furnace]

flashing light codes show "Primary/Secondary limit switch open"

I replaced the "limit switch" with one i ordered from SupplyHouse with the same spec [160-30f] and fired it back up and i still get the same error code. What should i try next? (trying to avoid spending $200 on a service call for a $12 part)

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thanks!