I have installed DCC and sound in about 60 locos. I have always saved the DC circuit boards, because ahem, I save everything. Is there any use for them? I do not plan to remove the DCC boards, and will likely never need the old DC light boards. Is there any use for them. I'm ready to pitch them out.
Old loco circuit boards that have lights attached could be made into test lights by soldering a pair of wires to the tabs that pick up power from the wheel wipers or loco frames. They can also be used to light the interior of structures.
If you have an electronics recycling program in your area, these boards could be turned in for recycling because they do contain copper and other recoverable metals.