Wiring the LEDs in a DC wired loco for DCC


I have a DC loco that has 4 LEDs front and rear. There are two white LEDs and two red LEDs at each end.

When running forward in DC mode the two white LEDS light up and two red LEDs in the rear light up and vice versa.
I would like to install a decoder into the loco but I am not sure how to wire the LEDs so that I get the same functionality.

The LED terminals are not all visible. I fact there are only 4 leads coming from each bank of LEDs.

I am not sure how to up load a diagram to show the existing wiring layout.
Is anyone able to assist me?

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