Google Analytics Cross Domain Tracking Conversion Referral Issue - google-analytics

Question

So I have two sites for a client, we'll say www.main.com is their main website and www.signup.com is a site where the user signs up for a certain service.
I recently switched signup.com over to universal analytics so that we could implement cross-domain tracking via the autolink plugin.
I used this article to help me set up the code on each domain.
Here is what I have on main.com:
<script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-11865301-1', 'auto', {'allowLinker': true});
ga('require', 'linker');
ga('linker:autoLink', ['signup.com'] );
ga('require', 'displayfeatures');
ga('send', 'pageview');
</script>
NOTE: I'm not sure what 'displayfeatures' is. I was told that a 3rd party vendor had to customize the code at one point and that I shouldn't remove anything.
And here is what I have on signup.com:
<script>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o),
m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)
})(window,document,'script','//www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-11865301-1', 'auto'), {'allowLinker': true};
ga('require', 'linker');
ga('linker:autoLink', ['main.com'] );
ga('send', 'pageview');
</script>
I also have both domains listed in my Referral Exclusion List so that we don't see main.com as referrals for the signup goal.
What's happening now though, is that for almost all of our conversions, the source/medium is showing as (direct)/(none) and the referral path is showing as (not set). We cannot figure out why.
At the time of this posting there are 14 goal conversions for the day. All of them are reporting a referral path of (not set) and 13 of them are reporting a source/medium of (direct)/(none). There is one conversion that has it's source/medium listed as bing/organic, if that is any kind of clue.
I'm not finding a lot of results on the subject in my googling so this is my last resort. Any help would be appreciated.
UPDATE: So I've been researching this heavily for the past 24 hours and have found out more information.
The (direct) or (not set) referral sources are coming from main.com. The reason they are listed as direct or not set referrals is because we have main.com listed in the referral exclusion list. When I turned it off these referrals started coming is as main.com.
It's starting to look more and more like there is no way to take the original referrer from main.com and carry it over to signup.com.
Can anyone confirm or deny this theory?

Answer 1

When you link domains for cross-domain tracking, they should all be included in the autoLink.
ga('linker:autoLink', ['signup.com', 'main.com'] );