There is a ground buzz on my thinline acuostic pickup except when i touch the jack

It is a definite pickup grounding issue causing hum/"buzz" which diminishes when touching strings. Check the impedance of cable jack inputs and cable which should be 1/4"mono input/output jacks) . A personal preference but effective is to NOT run guitar direct into mixer but through an external amp w/ a headphone out jack . Noise gating/preamp filter also will help eliminate the "buzz"/noise from pickups. It is unfortunately the nature of the "electro-magnetic" beast when it comes to electric guitar pickups .Hope this helps.

Try using a di box with ground lift switch

your pressumption would be correct. The Thinline 332 runs under the bridge saddle, and the Piezo is attached ti the inside of the guitar body, tilt your guitar and have a look inside, you may be able to see it.

Or a bad solder connection on the ground wire on the jack, or shell/sheild on the guitar.

Here is the list you seek.
http://www.gibson.com/en-us/Support/TechSupport/Wiring Diagrams/

Probably the ground wire is broken on this either at the jack or very near the end of th pickup stick. This acts like a condenser microphone and is fairly high impedance so any break in the ground will pickup hum. Using a high impedance guitar cable is necessary.

This may be strictly magnetic pickup from nearby sources of transformers, ballasts or other motors that generate these magnetic fields. Humbucker pickups have hum cancelling windings that PARTIALLY remove the hum. Wires from pickups to other components should be twisted to help cancel the problem.

This is a grounding and shielding problem. It is unknown what type of guitar you have but if there are other electronics, they need to be grounded to this device ground. Any source of magnetic fileds can worsen problems. Transformers in amps, etc. Solid body guitars have special shielding paint and you may be able to improve shielding by painting... just don't get it on circuit boards as it will short out the circuitry.

The cause is a lack of proper earth grounding in the 8 track so your jack-lead is acting like a radio aerial. The solution is simple - buy a Direct Injection (DI) box to place between the guitar and recorder.

You have a grounding problem ! You need to BOND (electrically connect) all the metal parts including the cases and shafts of the volume controls and switches. OFTEN the cavity with the controls are painted with a conductive paint such as Aquadag or NicklePrint which is then bonded to the barrel part of the jack you plug into. Note, while this helps the buzzing due to touching the metaal parts, it will not eliminate hum if you get your guitar pickups into a magnetic field from transformers, etc.

Several things to try:
- Probably already have, but another guitar cord.
- Ground switch on the amp?
- I had an older guitar that buzzed due to the pickups. While touching the strings, all was well - I was acting as the ground then. The ground wire broke, so it buzzed no matter what. The ground wire ran to the metal bridge.
- Play louder than the buzz! :)