Have a old yamaha guitar number 20309402 can you tell me anything about it

No, but you can try:

"Serial numbers can be extremely tricky," says Gibson Customer Service Manager Jason Davidson, whose team fields calls and emails regarding every Gibson division. "Some can tell you a lot about a guitar, and some don't really tell you anything. Gibson has had so many different schemes over the years, and now we're using reissue serial numbers that look like the old serial numbers."
Gibson Support Serial Number Search

As a guitarist myself, and from my understanding, Yamaha Pacifica guitars should have a "PAC" number on it. Check here for more info:
https://en.wikipedia.org/wiki/Yamaha_Pacifica

here is Yamaha 's Serial Number Wizard site. Yamaha Corporation of America
Also check out here..this is even better

Serial Number Chart For Acoustic and Classical Guitars

But in looking your number up I cant find a reasonable explanation. No letters...and there are 6 digit numerical numbers but they dont match yamaha's codes...I would call yamaha and talk to a tech at 1 (714) 522-9000 Good luck

go to Support Yamaha United States Contact and tell them your model and serial probably and they can get you the right preamp. Good luck APX Series Acoustic Electrics Guitars Guitars Basses Musical Instruments...

Can you forward some photos to me? Serial numbers and Kay guitars vary by the age of the instrument. Also can you take a photo of any label inside the sound hole or at least tell me what it says in there, where was it made, etc. I'll await your response.

It would help if you had identified the guitar maker and location of the serial number. I assume it's a Yamaha, but the serial number doesn't coincide with any of the typical systems they used. The first two numbers could be the year of manufacture, but the earliest Yamaha I could find was 1966, so you may want to go direct to Yamaha and ask if they recognize the number based on the model number.Yamaha Corporation of America
6600 Orangethorpe Ave.
Buena Park, CA 90620
(714) 522-9011 Email Inquires:[email protected]

Here is the link you need:http://europe.yamaha.com/en/products/musical-instruments/guitars-basses/el-basses/rbx/rbx374/?mode=model The manual is down loaded in pdf. Scroll down the page. The serial number has nothing to do with the manual only the model number applies.

60902313
Your guitar was made on
September 2nd, 1986 , 1996
or 2006
Production Number: 313
Source http://www.guitardaterproject.org/Yamaha.aspx

Try to open the back part of the guitar. The plastic plate covering and try to read and note down the types and serial numbers of the potentiometer, pick-up model, or anything that is noted inside.

Check www.yamaha.com/apps/guitararchives/guitarserial.html
It gives dates from old serial numbers