1. Consult your owner's manual: This is the best resource. It will have a diagram showing the location of each bulb and the bulb type (e.g., 3157, 1157, etc.).
2. Check the bulb packaging: If you've already bought replacement bulbs, the packaging should specify the correct type for your Jeep Liberty.
3. Look at the bulbs themselves: Once you access the taillights, the bulb itself usually has a number printed on it.
Without more specific information, I can't provide you with a single "brake light number".
