Just finished up on reversing the direction of the LEDs on a pair of MTH locomotive light boards.  It was no big deal because I had extra 0603 warm white LEDs on hand.  I questioned whether I should publish this but decided to anyway.  I’m sure any installer or I could do this for you if requested too.

The light board idea is not new.  Most manufacturers do it well and with a wider vision so that the positive polarity is common and feeds all of the LEDs and the negative leads each go to the electronic decoder light switch. MTH for some unknown reason decided to use the negative polarity as common.  MTH’s manufacturing technology for these boards is interesting also.  The LEDs are glued to the board prior to soldering.  I believe this is old technology.  It is also a further impediment to seeing the light.....

The LED removal procedure involves melting the solder and carefully prying the LED from the printed circuit board simultaneously.  (This is why I was glad to have the extra LEDs on hand.....)  Reversing the polarity (direction the LEDs are pointed on the printed circuit board) and reassembly is easy and straightforward.

Here is a picture of the two revised boards.

Above is a copy of my notes for the front board LED positions, leads and polarities.  A proper battery should be all you need to test the LED circuits.

Hope this helps!