Without specifics, I would recommend simplifying the situation by just using the absolute path to this external .js file, ex (you will want to use https on an ssl if this or the pages it's on are or need to be secure):
Code:
<script type="text/javascript" src="http://www.somedomain.com/scripts/abc.js"></script>
Put that in the head of each page, or better still, if you have a server side template, or head include, put it in there.
If it will always be on the same domain as your pages, the network path is preferable:
Code:
<script type="text/javascript" src="/scripts/abc.js"></script>
That way either protocol (if available) will be used as necessary.
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