Selected answers from the Dumb SEO Questions G+ community.
Tony McCreath: Google will follow it, and so will the "juice". However, I don`t think browser will. They will pop up the warning. So it can be a bad user experience if you still have links to it.
Neil Cheesman: Wouldn`t the 301 redirect occur before the SSL certificate? (and that is a question for someone with better knowledge than me on the subject and not a statement)
Stockbridge Truslow: Depends upon how the redirection is handled. Server side and MOST wordpress plugins, the redirect will happen before any TLS is established, though - so you should be fine.
Richard Hearne: Actually, this also depends on multiple other links in the chain. Your DNS, HTTP server and any intermediary systems are all hit before an interpreter like PHP (which would then run WordPress) is ever called. Basically, if anything in the chain enforces HTTPS, then the redirect to the alternative domain may not be seen before HTTPS handshake. Some examples: HSTS policy set in HTTP headers, HTTP server redirecting non-HTTPS requests to HTTPS, Cloudflare handling DNS and enforcing HTTPS at that point, the list goes on. So the comment above "Server side and MOST wordpress plugins" is entirely dependent on various other aspects in your set-up. A heck of a lot happens long before your request gets anywhere near PHP etc. or WordPress.