I am installing a DH165A0 in an Athearn SD70.
The head light outputs are a nominal 30 ma (with the link cut).
The bulbs were of course a bit lower in their current demands and were very bright for a short while.
Is there any way to lower the current output from 30ma or do I need to add a resistor in line with the bulb to drop the voltage output?
Of course if it is supposed to be a regulated current output this might be a problem.
The DH165A0 has a constant current source for F0F and F0R, so a series resistor will simply increase the terminal voltage at the selected fixed current.
To drop the lamp current, add a resistor in parallel with the lamp to bypass some of the current selected, calculating value for the resistor: (R = Lamp Voltage / amount of current to divert).
If the resistor is too small a value it will bypass more of the current and the lamp will be dimmer.
You can try a number of values to get the best "fit".