A Visteon serial number starts with the letter M (or sometimes Axx) followed by 6 digits, and is usually on the main label, although sometimes it could be stamped on the side.
Serial Number: M188845
Alternate Method
On some models, you can press buttons 1 and 6 together which will then show the pre-code. If you use this method, prefix it with an Mwhen you enter into our system.