Yeah it does work (facepalm) - It was the structure of my includes causing the issue. My final code:
<a data-toggle="modal"
data-target="#loginModal"
id="loginLink"
href="javascript:;">Login</a>
<a data-toggle="modal"
data-target="#loginModal"
id="registerLink"
href="javascript:;">Register</a>
<script type="text/javascript">
$("#loginLink").click(function(e) {
$("#tab_3_2").removeClass("active");
$("#tab_3_1").addClass("active");
});
$("#registerLink").click(function(e) {
$("#tab_3_1").removeClass("active");
$("#tab_3_2").addClass("active");
});
</script>
Thank you Jorge!