>>>
>>>Ok, the answer was the convoluted naming it had like paul suggested. It was also put in a strange place in the source. I was able to set the name of the master page in the master page init, and then between that and the content holder name I can use getElementById with that long name.
>>
>>Just be aware that if you happen to move things around, the name can change.
>
>Can you just pass ClientID to the JavaScript function ?

Yes, I've shown one way before by building/injecting the JS code from the code behind (using one of the Page.ClientScript.Register* methods in one of the other posts recently. You can also embed this in the ASPX part of the page using markup:

 var myField = document.getElementById('<%= ServerSideControlID.ClientID %');