The DH165L0 decoder F0F and F0R headlight functions are factory configured with an onboard current regulator for the factory-installed low voltage bulbs (or LEDs) when using a maximum DCC track voltage of up to 16Volts.
To bypass the current regulator and use 12V to 16V lamps with the DH165L0 on F0F and F0R, bridge each of the two pair of solder pads as shown on the back side of the decoder in the figure below.
The circuit board is marked with F and R adjacent to the soldering points.
Bridge between the two F points for a higher voltage bulb on the front.
Bridge between the two R points for a higher voltage bulb on the rear.
Once doing so, be sure to replace the yellow insulating tape on the decoder back and change the locomotive lamps to 12V to 16V bulbs.