A fun fact on '66 Fenders..... when I pulled the pickguard off mine, I saw "ES" stamped into the body. I assumed the bass had been previously owned by somebody with those initials who had stamped them in to identify in case of theft. I pulled the paragraph below off a web site:
1966 and the "ES" Stamp.
In 1966, Fender used the "ES" code a lot on their custom color instruments. At least for 1966, the ES code was used as some sort of default for custom colored instruments (be it Teles, or Strats or Jazz Basses). This two letters ("ES" for "Enter Special") seems to denote a special order, at least for 1966. Again this is has been seen lots of times on 1966 documented original custom color instruments. I have also seen the "ES" stamp on some 1966 sunburst instruments! (Perhaps these guitars were special show models, so extra care was taken in their finish.) The 1/2" tall 2-letter code were a factory color code, and are completely different than the 1/2" tall three-digit codes. The two-letter code appears to be CBS/Fender's way of specifying bodies to be painted a custom color for a special order once the body was in the spray booth. If a guitar has a two letter code on the body *only* (and not the neck), again this confirms the 2-letter code was an original factory color code (and does not indicate a factory refinish order). But then there is this question: why do only some 1965-1968 custom color Fenders have this two letter code and others do not? It may have to do with how many custom colored guitars were being painted at any point in time, and the 2-letter code was applied to avoid confusion. Or it was applied just for particular special orders (like a Fender NAMM show guitar or a special dealer/artist order).
...and there it is!!
The pots...
The pickups...
The neck heel, pocket, and plate...