can anyone tell me why this script i've pieced together will disable radio buttons but will not re-enable them?

The script code:

<SCRIPT>
function yes(trigger) {
if (trigger = 'false')
{disableDiv.style.color ='black'; disableDiv2.style.color ='black';}
else
{disableDiv.style.color ='grey'; disableDiv2.style.color ='grey';}

<!-- mainform.conditionalid.disabled=false; for text boxes
<!-- mainform.conditionalid.disabled=true; for text boxes - under disable
<!-- mainform.conditionalid.value=''; under disable

for (var i=0; i<mainform.elements.length; i++) {
if (mainform.elements[i].name == 'JointEff') {
mainform.elements[i].disabled = trigger;
}
}
}
</SCRIPT>




The complete code:


<html>
<head>
<SCRIPT>
function yes(trigger) {
if (trigger = 'false')
{disableDiv.style.color ='black'; disableDiv2.style.color ='black';}
else
{disableDiv.style.color ='grey'; disableDiv2.style.color ='grey';}

<!-- mainform.conditionalid.disabled=false; for text boxes
<!-- mainform.conditionalid.disabled=true; for text boxes - under disable
<!-- mainform.conditionalid.value=''; under disable

for (var i=0; i<mainform.elements.length; i++) {
if (mainform.elements[i].name == 'JointEff') {
mainform.elements[i].disabled = trigger;
}
}
}
</SCRIPT>
</head>
<body bgcolor="#FFFFFF" text="#000000">
<form name="mainform" action="budgetquote3.asp" method="POST">
<table width="100%" border="0" cellpadding="0" cellspacing="0" bordercolor="#666666">
<tr>
<td height="57" valign="top" colspan="2">
<p>Do You Want To Select Joint Efficiency?
<input type="radio" name="selectje" value="radiobutton" onclick="yes(false);" CHECKED>
Yes
<input type="radio" name="selectje" value="radiobutton2" onclick="yes(true);">
No</p>
<p>&nbsp;</p>
</td>
</tr>
<tr>
<td height="28" width="176" valign="middle" align="right" bordercolor="#FFFFFF">
<DIV ID="disableDiv" style="color:black"> Top Head: </div>
</td>
<td width="815" valign="middle" bordercolor="#FFFFFF">
<DIV ID="disableDiv2" style="color:black">
<input type="radio" name="JointEff" value="radiobutton">
70%
<input type="radio" name="JointEff" value="radiobutton">
85%
<input type="radio" name="JointEff" value="radiobutton">
100% </div>
</td>
</tr>
</table>
</form>
</body>
</html>