[Thinkpad] Auto adapter for A-series

[david.stickney]

I found I could run my 770 direct from the lighter socket (you need to make
an adaptor - solder a 2.5mm power plug onto an old charger lead - centre
core is +12v at each end).  The battery wouldn't charge, and I seem to
remember it wouldn't power up unless I removed the TP battery completely.
But then it worked perfectly.  This was with the engine stopped and the car
battery volts are 12v.  With the engine running, the voltage is more like
14v, and everything worked fine with this slightly below the required 16v
from the brick.
Dave