You can either call Gold Medal at 1-800-543-0862 or fix it yourself. There are only 3 wires going in. 2 are hot and 1 is the ground. All you need is a volt meter to determine the ground, and the other wires hook up as follows: 1 wire goes to one side of the heat element, the other wire goes to one spot on the thermostat. Then there's a jumper wire between the heat element and the thermostat.

I actually just had a pleasant experience contacting Hellman Group, (The manufacturer of Nostalgia Electric popcorn machines). I called the main number, pressed 1 for customer support, and after 3 tries (got an answering machine the first couple of times), I got someone in customer service who was able to help me get the part I wanted. Not sure if they can give you a wiring diagram.
The Helman Group, Ltd.
1621 Beacon Place
Oxnard, CA 93033

• tel: 805.487.7772
• fax: 805.487.9975
• info@helmangroup.com