Move includes/templates/template_default/templates/tpl_product_info_display.php
to your own template directory, if it's not already there.
In this file, find: <!-- eof Product details list -->
On the following line, insert this block of code:
<span id="productQuestions" class="biggerText">
<br />
<b><?php echo '<a href="' . zen_href_link(FILENAME_ASK_A_QUESTION, 'products_id=' . $_GET['products_id'], 'SSL') . '">' . ASK_A_QUESTION . '</a>'; ?></b>
</span>
<br class="clearBoth" />
Alternately, you may use the button provided. To do this, insert
<div id="askQuestion" class="biggerText">
<?php echo '<a href="' . zen_href_link(FILENAME_ASK_A_QUESTION, 'products_id='
. $_GET['products_id'], 'SSL') . '">' .
zen_image_button(BUTTON_IMAGE_ASK_A_QUESTION, BUTTON_ASK_A_QUESTION_ALT) .
'</a>'; ?></div>
<br />
<br class="clearBoth" />
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