Here is my latest conversion of a flat bed waggon from USA Trains with a “FRED” flashing light.

The “FRED” can be obtained from Easygleis .

Power is supplied by 4 CRC 2032 Lithium batteries.
These come in a flat 2-piece case with switch, which I found on eBay.

You have to mill away a lot, but that doesn’t detract from the wagon’s stability.
I first painted over the milling surfaces with a simple brown varnish, the matching color I still get!

If you want to know what a FRED is, look here.