BMW 3.0 CSE

There are 350 DC volts of Telsa LiIon batteries in my car but I need a 12 volt source to kick off the electronics that energize all the complex systems such as the precharge controller and traction contactors.  Therefore, I use a small LiIon 12v battery designed for a motorcycle.  The problem is, I keep some things, like my Raspberry Pi gauge computer constantly running so that everything works instantly at the turn of the key and that drains the little 30 Ah battery pretty quickly, like in a day or two.

The car is running but there are a lot of electrical gremlins that I need to find and fix.  Now that I have the car home, I'll have time to work on all these.  

You've read about the fancy digital dash app I've written that displays all sorts of information on a display in the hole that used to belong to the tachometer.  But that still leaves four other analog gauges in the instrument panel: The speedometer, clock, fuel, and temperature gauges.  These are old school VDO gauges that just look proper and cool so I want to make them all work with this new digital vehicle.

Recall, I'm trying to add a digital dashboard display in the round hole normally filled by the tachometer of the stock BMW instrument cluster.  It is a gorgeous set of VDO instruments set in a French walnut real wood cluster.  I want to keep as much of the original look as possible but there is no need for a tachometer.  The speed of the Tesla motor is many times faster than a gas engine and basically irrelevant.  Instead, I'd like to know what gear I'm in, the state of my batteries, the most critical temperature of the components, my remaining range, output power, etc.

Gear selection in a Tesla drive unit is done electronically.  That's why so many electric cars have gear buttons instead of gear levers -- there's nothing physical that needs to move.  But, in trying to keep the original BMW aesthetic, I want to use the stock automatic transmission shifter to send signals to the Tesla drive unit.