If you have changed the shop$config.asp file and updated Xssl to use HTTPS url of your site and changed xsslshopcustomer config to Yes, and you still see that the customer registration page (shopcustregister.asp) is still not in HTTPS, then you can follow these steps below to make it displays as HTTPS:
1. Open the file
shopcustregister.asp using notepad or text editor.
2. Locate this code :
<!--#include file="shopmailformattemplate.asp"-->
<%
Response.Buffer = True
If (Request.ServerVariables("HTTPS") = "off") Then
Dim xredir__, xqstr__
xredir__ = "https://" & Request.ServerVariables("SERVER_NAME") & _
Request.ServerVariables("SCRIPT_NAME")
xqstr__ = Request.ServerVariables("QUERY_STRING")
if xqstr__ > "" Then xredir__ = xredir__ & "?" & xqstr__
Response.redirect xredir__
End if
%>