This works without SSL as well.
Here's my working config, it be of might help..
bindDN = CN=ldapquery,OU=Services,DC=test,DC=com
bindDNpassword = aPassword
charset = utf8
groupBaseDN = CN=Splunk_Admins,OU=Groups,DC=test,DC=com;CN=Splunk_Power_Users,OU=Groups,DC=test,DC=com;CN=Splunk_Users,OU=Groups,DC=test,DC=com
groupMappingAttribute = dn
groupMemberAttribute = member
groupNameAttribute = cn
host = testDC.test.com
nestedGroups = 0
network_timeout = 20
port = 389
realNameAttribute = cn
sizelimit = 1000
timelimit = 15
userBaseDN = OU=Users,OU=MyUsers,DC=test,DC=com
userNameAttribute = samaccountname
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