How do I specify the desired load balancer for my ECS service?

I've got an AWS ECS service setup. I've also got a load balancer configured on the EC2 side of things. The EC2 instances are up and running and the load balancer is ready to go. When I create an ECS service, I do not see where I choose to use a certain load balancer. I go through the create menu and then when all is created, I see that there are no load balancers on the service detail view.

How do I configure the ECS service to use my existing load balancer?