I think you are right . I also seem to remember such a part connected to the vacuum hose & plugging into a grommet built into the booster .

I did find this sensor on RockAuto.com , but have no idea if it is related to your problem ?

More Information for AIRTEX / WELLS 5S7870

Have you seen such a sensor ? If so , you might , VERY CAREFULLY , try unplugging the electrical connector & see what the results would be ? Be prepared to use the parking brake , if you try this .

Photos , please ?

God bless
Wyr