Chosen Solution

Most detectors have a telephone style power cord connection. How can I connect to the USB power on my BMW motorcycle?

If I correctly understood, you would like to place a USB port on you motorcycle, in that case you need to step down your battery voltage from 12V to 5V using a regulator, or you can buy a converter like this one :

But you need to make some modifications, the best solution is to put a power bank in your pocket.