I have a merged RH2019 project, with the merged project comprised of 20 individual projects. All the individual projects are at the same directory level. In 11 of these projects, I have a common topic that details a particular dialog box and all the options on all the tabs on the dialog box.
I created the necessary topics (5 in total that addressed this dialog box - one for each tab on the dialog box) in the default merge project for my merged help, and then I attempted the following in one of the projects that also required this topic:
1.) In my TOC, created a new page entry.
2.) In the Properties for this new page entry, for the Source, clicked on the Update Link URL icon and on the Update Page dialog box that opens, I select Local Files.
3.) I then click the Browse icon next to the File Path field, and I browse to and select the local topic file.
4.) I click Done and then Apply.
And zip, zilch, nada . . the topic page remains even if I close and re-open it. If I copy these common files to each project location, and make them project files, then when I link to them, the topic page is populated as expected.
This doesn't help me - I need to be able to link to local files as I want to write these files only once and then link to them as I need - it keeps all these files in sync in each project and I don't have to worry about updating in multiple places, or at least updating in one place and then copying down to all the projects that require them - i.e., single sourcing!!!
What am I missing/not understanding about linking to Local Files?
Correcting a typo - left out the word "blank" when describing what happens to a topic page if I attempt to link to a local file - one not contained in the project.
And zip, zilch, nada . . the topic page remains Blank!!!
Have a look at Peter's site and make sure you have things set up the recommended way. It makes things much easier. You can download a demo to see how it all works at the bottom of the page.
There is no concept of a default project in merged help, there is a parent and there are children. One of the children may be your main child but it is not a default. I mention this in case anyone thinks you are referring to the parent when you use the term default.
Prior to 2019 New UI to have a topic from one project appear in the TOC of another, the solution was a redirect. See http://www.grainge.org/pages/authoring/merging_webhelp/merging_toclinks.htm
I have found another solution but you might decide the above is still the best solution as there is a bug but one that can be worked around.
I created a Common Topic in Child One and then in the other child projects creating a Linked_Topics folder and linking to that topic. The bug is that the linked topic does not show the CSS from the source child. The path is wrong. You can easily select the required CSS in the second and subsequent child projects.
There is a further issue in that if you update the original topic, the child projects will show the topic as being out of sync, as they should, but when you sync, you will need to correct the CSS attached to the linked topics.
Try that and let us know if it solves the issue.