Originally Posted by SlowerOne

This ridiculous speculation really has to stop, as it makes no sense in any form of engineering - electrical, electronic or mechanical!!

Let's see if this kills it off...

When a receiver pack is plugged into the receiver, the positive and negative are directly connected to the positive and negative of the speedo by the rails under the receiver pins. What's the difference between that direct connection and the one you are all speculating over in the BD? That'd be... none!

BD have very cleverly provided you with a socket to plug in a power supply for the car electronics that can use the regulator already built into the speedo. It is doing nothing more or less than plugging that same pack into the receiver, and saving you the cost and complexity of a regulator for the Rx pack. Period. End of...