This is an updated version of 2 x domains for same site in Google make canonical or not and I am posting it again as A) there is a new SSL aspect to the question and B) it's nearly 4 years old and things change.
To recap the current situation, a site launched in 1999 with a domain consisting of two, very descriptive words (let's say dog-toys.ie). In about 2001 I parked dogtoys.ie onto dog-toys.ie (client had radio ads and figured the dash may add confusion to the site name). Also, for both domains, we have not made www canonical so www.dogtoys.ie/example.html or dog-toys.ie/example.html are the same page.
Based on advice here in March 2014 we did nothing and site continues to do well in Google. Searches show both domains have fairly even indexing:
site:dogtoys.ie About 3,500 results site:dog-toys.ie About 3,040 results
We are re-visiting this because of the general move to SSL which now factors into ranking, and browsers give a not secure warning on forms.
Any advice / thoughts please - could we loose ranging by combining the domains?