If Aqua Signal it's a Twist-Lock
If your anchor light is Aqua-Signal it's a twist-lock. Take a firm hold of the lens and gently twist it and lift up. Don't remember which direction but there are only two choices.It's been my experience that most reasons for the anchor light (or steaming light for that matter) not working is due to corrosion or wiring connections (which also may be due to corrosion). If it were new, or if you can clean the corrosion, put on some dielectric grease on all the contact points as well as the wiring connections. Web site: http://www.aquasignal.net/ and http://www.aquasignal.de/index1.html (this is the better one)