The light could also "dim" because of the amp load on the switch itself...an indication of some "restriction" going on with the window assembly.
You did say you just replaced the regulator, but maybe something else is amiss with the assembly?
Anyway, I have the same Radio Shack TV tuner spray as longston just described, and it works well on electrical contacts (especially old corroded or oxidized ones like in my 73 Bug).
Try the spray first...it's quick and easy to do, and will eliminate that being a problem before you decide to crack open a door panel...
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car