Hello! :) Actually, you do NOT need a pendulum to speak to spirits!
All a pendulum does is tell you 'yes' or 'no'. Thats it. It has absolutely nothing to do with guardians, spirits, ghosts, gods and goddesses, or anything.
I have been using a pendulum very successfully since I bought it at the store yesterday. (Be very careful where you buy them!!!) It has worked wonders for me!
I also have a ghost friend. He has nothing to do with my pendulum.
I do not have my guardian spirit, and yet my pendulum still works wonders. You do not need a ghost to use a pendulum. The energy that makes it move is drawn from the Universe itself, which is all around us. (I am psychic so I read into the connection hehehe)
The pendulum uses your own energy(chi) to gather intentions and vibration to be able to coordinate the answer. (you must be calm and centered to use it)
Once it gathers your own information, it ('it' being the universe itself) uses your chi to come up with the answer. Being the infinite universe, it is able to travel through the constraints of time and space effortlessly, gathering information from your past and future. (based off of the present course of action, of course you can change future events if you prevent them by changing the course of action)
Does this help? Pendulums have nothing to do with spirits, guardians, or ghosts. All three of those topics are completely seperate, although I suppose you could use them in conjunction.