LED fuel indicator instead of halogen
The LED isn't a heavy enough load to pull the voltage down.  Apparently whatever was driving the halogen can "leak" a bit, and the designers thought it was okay because the halogen wouldn't show it.

For a quick solution, you could put a second resistor in parallel with the LED/resistor combination that is roughly the same or slightly higher resistance than the halogen was.  Note that halogens, like incandescent bulbs in general, increase their resistance when they get hot, so you might want to account for that by a factor of 2 or 3 from the cold measurement.  Also don't forget to handle the power as Watts = Volts^2/Ohms.

Or you could redesign the driving circuit to allow a lighter load.