Think I have partially solved my own problem. I removed the ajp connector from the server.xml so http is the only option and mod_cluster began using http.
Eventually I need to have both the http and https connectors running. How does the mod_cluster JBoss service decide which protocol to broadcast to the http proxy?
If an AJP connector, or connector using a reverse connection exists, mod_cluster will prefer it. Otherwise, mod_cluster chooses the connector with the highest value for maxThreads.