Parse variable from current URL into iframe

Parse variable from current URL into iframe

I cant seem to get the code right to get the variable from a non-zoho-based URL into an iframe
for instance a person has come to my website from an adwords campaign, which as put them on a landing page with the following address www.MySite.com/AdCamp=ID2

the page itself is built in Wordpress and has zoho iframe snippet on it.  I want the zoho form (within the iframe) to accept the variable ID2 from the URL and populate the value in the field called "referring_source" in the embedded form.

How would i accomplish this?