I figured it out: Go to plug Ins. Click on the Edit button under the ‘Aweber Web Form Widget’ plug in.
It will show you the actual code for the plug in. On the right, click to select aweber_webform_plugin.php
Then hit CTRL-F to find ‘http’. The fourth and six instances of ‘http’ link to ‘http://forms.aweber.com…..’
For both instances, add the ‘s’ for secure at the end of ‘http’ so they read ‘https://forms.aweber.com/….’
Click on SAVE and you are done.
