You should feel the two metal nubs inside the 1-1/2 inch wide hole. The should be there and have spring tension. If they are bad you need to replace the inlet. If they are good then remove the inlet and see if the low voltage wires are connected. You can use this video to help you understand inlet removal. https://builtinvacuum.com/cvtv/tips/replace-inlet-steps.html. Having said all that, you may have the proprietary 4940 inlets. If so, there will be some differences.