Referencing a field on a vendor record FROM an item record

OK all you scripting pro’s. I’m starting to cut my teeth into the scripting world and have run into an issue.

I have what I THINK is a pretty simple question but can’t seem to figure it out.

HOW do you access a vendor subrecord FROM an inventory record?

I have a field on the vendor record that I want to check after the vendor has been sourced on the item record.

Here is what I have so far:

function postSource(type,name)
{
    var testEnable = nlapiGetCurrentLineItemValue('itemvendor', 'custentity_loc_01_inv_enable_ven');
    alert("testEnable= " + testEnable);
}

this SHOULD get me the value of the field on the vendor record but no matter what I do it comes back as