For my 2018 MS, I bought a standard OBD2 extension cable, localized the 12V source and crimped the ends to connect my device. I just plugged it straight into the port. Actually, now that I think about it, I did the same thing on my 2016 MS. Both times, the OBD port was located in the footwell, under the driver's side dash.Don’t you need an adapter cable from the propriety Tesla port to the standard OBDII port?
Here is what I bought: https://www.amazon.com/gp/product/B007PAHHWM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1