External links are going through a 'confirmation'/'logging' process which are done at "http://go.forum.grasscity.com", and even when you're using HTTPS version of the website, this part of the website is still running on HTTP by default(currently). Here is the example of a post which in HTTPS version of grasscity and also linked to an external HTTPS website as the target page: https://forum.grasscity.com/lighting/1393273-what-...
I've checked that again and looks pretty fine. (no redirection to go.forum.grasscity.com though) Good job