On 25/05/2017 11:45, Harry Bloomfield wrote:
Lee has brought this to us :
Plus the ability for the BCM to substitute a failed lamp for an
alternative is quite useful. If sometimes confusing

Mine can substitute a brake light fed on a lower voltage for a failed
tail light.

More likely it is using pulse-width modulation - far easier for digital
and power electronics than varying the voltage.

SteveW