[JRTJH]

Yup, that's what's under the cover. It's a "auto-reset 12 VDC circuit breaker"... That's what's "under the cover" Here's what it looks like "with the cover".... About $5 at any RV parts store. Buy a new "red cover" if it doesn't come with one. Another $1, but well worth it. When you reinstall it (it looks like the screw and part of the mounting tab is shown in the first photo) don't tighten the screw too much or you'll crush the tab and it will break again.

Be sure to look carefully at how it's connected. There is a "hot side and a protected side" usually marked BATT and LOAD. Don't hook it up backwards, although it will still work, it doesn't protect the circuits if there are two or more in series. Usually, on Keystone RV's you'll find two mounted very close together. One for "main power" and one for the slides/jacks.