Well a Pendulum works like automatic writing you can invite your ‘Higher Self’, Angels etc… to work with you on divination (I’ve explained a bit in a thread):
Now if you want to use it in a ritual with a specific being. You can do the evocation and charge the Sigil. Then when you invite the Spirit, say that you want to do divination with the Pendulum (don’t forget to cleanse, it’s mentioned in the thread by @Anassa). Lay the sigil on your table and go over it with the pendulum. If you’re doing it right you will notice the difference right away (strong spirit).
This way it’s not your higher self that influences.
If you want to focus on hearing a spirit instead of a Pendulum trust yourself. If you ask a question, an answer will come in fragments in your mind, inner voice or if you ask in a dream.