Just to avoid any confusion here, the volumes and page numbers found in the
civil registration index (e.g. on FreeBMD) are not relevant when looking at the records at Essex Ancestors, which are
parish marriage registers and do not use that numbering system.
After 1 July 1837 the
content of the parish marriage record on Essex Ancestors should be identical to the civil registration record, except that the parish copy will show original signatures of spouses, witnesses and clergy.
As regards
Maldon registration district, this mapping site might help you to get orientated.
http://maps.familysearch.org/Enter the keyword
Maldon.
From the search results, select
Civil Registration District - Maldon.
On the map, select
List all Parishes in Maldon civil registration district, and a list will appear in the left-hand panel.
You can then use this list to direct your searches through the parish registers on Essex Ancestors.
You may want to bear in mind that if the marriage took place in a
register office or in a
nonconformist venue not covered by Essex Ancestors, you will not find it online. The only option then is to purchase the civil registration certificate from the GRO, using the volume/page reference found in the civil registration index (e.g. on FreeBMD).
http://www.freebmd.org.uk/http://www.gro.gov.uk/gro/content/certificates/default.asp