Ethnocentrism and cultural relativism do not have much in common. Ethnocentric ideas tend to negate the possiblity of a belief in cultural relativism.
Ethnocentrism is the idea that the way things are done in our society is superior to any other way of doing things. This sort of an attitude is clearly incompatible with cultural relativism. Cultural relativism holds that nothing is right or wrong and that things only have whatever value is given to them by a particular culture. In such a view, the traditions of all cultures are equally valid.
Ethnocentrism is a view that holds that one's own society is better than all others. This is completely opposed to the idea that all cultures are equally valid.