Black Headshell, AT-3600L Magnetic Cartridge Stylus Fit for Technics SL D1, SL D1K, SL D2, SL D202, SL D205, SL D2K, SL D3, SL D303, SL D33, SL D3K, SL D5

Start googling and get some step by step help. There are four wires going into your tone arm from the cartridge, two for each stereo channel. One could be loose or the pin is corroded or who knows what. Id get a cheap new cartridge and headshell to pop on and test if you don't get anywhere with your current one. You can buy a generic headshell and very decent starter cart for about $30 on Amazon. Then you could want to upgrade of figure it out from there https://www.amazon.com/dp/B0DSS13P2R