can anyone help me with the line under the dashboard of my 71 cutlass supreme?

 

I moved your post to a new thread because it was an unrelated question tacked onto an old thread. You are more likely to get a response with a new, current thread. Also, it's not possible to provide a helpful answer without more info. A/C cars used vacuum lines under the dash to control the flapper doors in the HVAC box. Does this car have A/C? The power trunk release was vacuum operated for some years. Does your car have a power trunk release? An aftermarket vacuum gauge would have had a vacuum line under the dash. Could your car have had one of these? Our mind reading device still isn't working.

 

It goes to the fitting.