If you are trying to install this on Zen-Cart 1.5.5f with the template Responsive_Classic (and probably some other responsive templates) and keep getting a white page, the reason is that Responsive_Classic needs to run jscript in the html_header.php file and CSS/JS Loader has moved all JQuery loads (including the base file) to the end of the <body> of the page.

Therefore when the script in htm_header.php tries to run it fails.

Specifically this:
Code:
  <script type="text/javascript">document.documentElement.className = 'no-fouc';</script>
Therefore, whatever you do below, make sure it is in the html_header.php file above that section of code.

Here are 3 fixes (don't do all three, just pick one):
1) Use your programming skills to move the html_header.php script out of the header. Then post how because I'm not skilled enough to do it and suspect it isn't possible without changing the entire template structure.

2) Since the JQuery Core should probably load on every page, and it is needed for the script in html_header.php, add back to html_header.php the code for loading the JQuery core. That means put this:
Code:
<script type="text/javascript">window.jQuery || document.write(unescape('%3Cscript type="text/javascript" src="//code.jquery.com/jquery-1.12.4.min.js" integrity="sha256-ZosEbRLbNQzLpnKIkEdrPv7lOy9C27hHQ+Xp8a4MxAQ=" crossorigin="anonymous"%3E%3C/script%3E'));</script><script type="text/javascript">window.jQuery || document.write(unescape('%3Cscript type="text/javascript" src="<?php echo $template->get_template_dir('.js',DIR_WS_TEMPLATE, $current_page_base,'jscript'); ?>/jquery.min.js"%3E%3C/script%3E'));</script>
somewhere in the file (not inside php tags). It is already minified so no worry that it isn't in the CSS/Loader. In your auto loaders make sure you aren't calling for another JQuery Core to be loaded.

3) Load all the JS loader/minified files in the header. Take the code that is specified as going in the tpl_main_page.php file (the JS loader code) and instead put it in html_header.php under the other code (the CSS loader code) you already added. Remember to remove it from tpl_main_page.php if you previously added it there.