I ended up having to open mine to add a ground wire. That bulb is under the top half of the case. It's been a while since I've been inside but I believe the cover over the bulb just lifts up (I recall having to carefully keep everything in place when adding that ground as stuff could get loose. I can't remember if it's part of the arm too). Since they can burn out, they have to be accessible.
Right out of the manual:
"Replace pilot bulb with #51 for 6 volt, #53 for 12 volt, or #356 for 24 volt service."
Below is an image inside mine (where I was adding a yellow ground). The blue wire is the pilot light.
