In most cars, there is an integrated antenna for all wireless signals. For example:
- Audi: https://parts.audiusa.com/p/Audi__/Mobile-Phone-Antenna/78750936/3G9035534.html
- GM: https://parts.gmparts.com/product/gm-genuine-parts-mobile-telephone-and-telematics-antenna-22964579
- VW: https://parts.vw.com/p/Volkswagen__Jetta/Mobile-Phone-Antenna/78750936/3G9035534.html
These are often mounted behind non-metallic surfaces (plastic bumper, spoiler, etc). You can try to cover them up, but it means you’ll lose all the other antenna functions.
Disconnecting at the other end can only take out cellular without affecting wifi, Bluetooth, etc.
Mind you, it’s not easy. There’s a wiring harness with a waterproof connector that eventually goes into the cell modem. You’ll have to find the right antenna pin and disrupt the signal. Different for every make/model and not possible without proper schematics.
WTF? 😳