And another video I just found: Sonic Youth’s Lee Ranaldo talks about the Jazzmaster (and his signature model), see the video right after the click:
How old is my instrument?
For a first hint, check the Serial-Number against the lists provided by Fender: http://www.fender.co.uk/support/product_dating.php
Better estimations require some fiddling in the insides of the guitar, look for stamps on the neck-heel, numbers in the neck-pocket and stamps on the potentiometer-housings. Lists with references can be found all over the web. A very valuable source of information is Jim Shine’s collection of Fender-parts: http://www.guitarhq.com/fenddiff/






