my 1999 3000 gt stereo is asking for a code and dont know it. how can i get it to work?

Have you contacted Mutsubishi Motors? You may be able to give the VIN and they might help you. Or you can ask the previous owner for it. Some people might write it down in their manual or on the back of the stereo. You will need the code every time the battery dies or gets disconnected.

From the factory the 3000GT came with a red "credit card" labeled ANTI-THEFT SYSTEM which had the 4 digit code you need. If you cannot locate that, check the owners manual. People typically wrote the code on the cover (front or back) or on the Radio Re- programming instructional page. If all that fails go to the website below and follow the prompts. You will need your VIN, Radio Serial Number and Radio Part Number. The last two numbers will be on the back of your radio, so you will have to remove it. https://www.mitsubishicars.com/owners/support/radio-code