Этот код работает для меня, это то, что вы впервые опубликовали (html) с кодом JavaScript, который должен делать то, что вам нужно. Разве это не работает для вас?
<div class="row">
<ul id="tabs" class="nav nav-tabs htabs">
<li class="active">
<a href="#tshirt" id="tshirt" value="TSHIRT" data-toggle="tab">T-shirts</a>
</li>
<li class="active">
<a href="#jacket" id="jacket" value="JACKET" data-toggle="tab">Jackets</a>
</li>
</ul>
</div>
<div class="tabs-content">
<div class="tab-pane tab-content active" id="tshirt">
<div class="row">
<div class="xs-50 sm-50 md-33">
<select id="size" class="form-control">
<option value>--Select size--</option>
<option value="xl">XLarge</option>
<option value="xxl">XXLarge</option>
</select>
</div>
<div class="xs-50 sm-50 md-33">
<select id="color" class="form-control">
<option value>--Select color--</option>
<option value="red">Red</option>
<option value="blue">Blue</option>
</select>
</div>
<div class="button-group btn">
<input id="submit" class="btn" name="submit" value="Search" type="submit" onclick="myclick()">
</div>
</div>
</div>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
<script>
function myclick() {
var url = window.location.href ;
var hash = url.substring(url.indexOf("#")+1);
var mysize = document.getElementById("size").value;
var mycolor = document.getElementById("color").value;
window.location.href = "http://www.test.com/?tab=" + hash + "&Size=" + mysize + "&mycolor=" + mycolor;
}
</script>
Обновленная версия
<link href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/css/bootstrap.min.css" rel="stylesheet" />
<div class="container">
<div class="row">
<ul id="tabs" class="nav nav-tabs htabs">
<li>
<button type="button" class="btn btn-link" onclick="mytype('TSHIRT')">T-shirts</button>
</li>
<li>
<button type="button" class="btn btn-link" onclick="mytype('JACKET')">Jackets</button>
</li>
</ul>
</div>
<div class="tabs-content">
<div class="tab-pane tab-content" id="tshirt" style="display:none">
<div class="row">
<div class="xs-50 sm-50 md-33">
<select id="tshirtsize" class="form-control">
<option value>--Select size--</option>
<option value="xl">XLarge</option>
<option value="xxl">XXLarge</option>
</select>
</div>
<div class="xs-50 sm-50 md-33">
<select id="tshirtcolor" class="form-control">
<option value>--Select color--</option>
<option value="red">Red</option>
<option value="blue">Blue</option>
</select>
</div>
<div class="button-group btn">
<input id="submit" class="btn" name="submit" value="Search" type="submit" onclick="myclick('tshirt')">
</div>
</div>
</div>
<div class="tab-pane tab-content" id="jacket" style="display:none">
<div class="row">
<div class="xs-50 sm-50 md-33">
<select id="jacketsize" class="form-control">
<option value>--Select size--</option>
<option value="sm">Small</option>
<option value="l">Large</option>
</select>
</div>
<div class="xs-50 sm-50 md-33">
<select id="jacketcolor" class="form-control">
<option value>--Select color--</option>
<option value="red">Red</option>
<option value="blue">Blue</option>
</select>
</div>
<div class="button-group btn">
<input id="submit" class="btn" name="submit" value="Search" type="submit" onclick="myclick('jacket')">
</div>
</div>
</div>
</div>
</div>
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.0/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.0/js/bootstrap.min.js"></script>
<script>
var passtype;
function mytype(mytype) {
switch (mytype) {
case "TSHIRT":
passtype = "TSHIRT";
document.getElementById("tshirt").style.display = "block";
document.getElementById("jacket").style.display = "none";
break;
case "JACKET":
passtype = "JACKET";
document.getElementById("jacket").style.display = "block";
document.getElementById("tshirt").style.display = "none";
}
}
function myclick(mytype) {
var url = window.location.href ;
var mysize = document.getElementById(mytype + "size").value;
var mycolor = document.getElementById(mytype + "color").value;
window.location.href = "results&searchfilter=category['" + mytype + "'],size['"+ mysize +"'],color['"+ mycolor +"']";
}
</script>