Validate Zip vs Validate Soc Sec

Hi all,

Rookie here wondering if anyone could help me on my last day of work. (Fri) I have to turn this code over to someone else and it does work exactly right.
Here is the problem:
Validate Zip works great, checks for proper length as well as allowing only numbers to be entered in.
SSN_check has the same check that won't allow you to enter characters, but it doesn't work. Exactly the same code here, but one works and one won't. Did I call it wrong? Thanks for any suggestions.

function SSN_check(field, len){
var valid2 = "0123456789";
var hyphencount2= 0;

if (field.length !=len) {
alert ("Your Social Security Number entry should be 9 digits.");
return;
}
for (var i=0; i < field.length; i++) {
temp = "" + field.substring(i, i+1);
if (valid2.indexOf(temp) == "-1") {
alert("Invalid characters in the Soc. Sec. Number. Please try again.");
return false;
}
return true;
}}
// end -->

<!-- This function works perfectly.

function validateZIP(field) {
var valid = "0123456789-";
var hyphencount = 0;

if (field.length!=5 && field.length!=9 && field.length!=10) {
alert("Please enter your 5 digit or 5 digit+4 zip code.");
return false;

}
for (var i=0; i < field.length; i++) {
temp = "" + field.substring(i, i+1);
if (temp == "-") hyphencount++;
if (valid.indexOf(temp) == "-1") {
alert("Invalid characters in your zip code. Please try again.");
return false;
}
if ((field.length ==9) | | (field.length == 10)){
if ((hyphencount != 1) && (field.charAt(5)!="-")) {
alert("The hyphen character should be used with a properly formatted 5 digit+four zip code, like '12345-6789'. Please try again.");
return false;
}}
}
return true;
}
// end -->

BODY...

Soc. Sec. Number: <input type= "text" name ="SSNum1" onKeyUp="return autoTab(this, 3, event);" size="4" maxlength="3" value="" onchange = "SSN_check(SSNum1.value,3)">-<input type= "text" name ="SSNum2" onKeyUp="return autoTab(this, 2, event);" size="3" maxlength="2" value="" onchange = "SSN_check(SSNum2.value,2)">-<input type= "text" name ="SSNum3" onKeyUp="return autoTab(this, 4, event);" size="5" maxlength="4" value = "" onchange = "SSN_check(SSNum3.value,4)" onFocus="nextfield ='Last_name';">

Zip:<input type= "text" name ="Zip" size=10 maxlength=10 value = "" onchange="validateZIP(Zip.value)" onFocus="nextfield ='Phone_a';">