I think you need a flasher circuit. When I saw the Sunrise guys at the '04 train show, they were next to the Richmond Controls guys, and he was selling the FRED circuit.
Come to think of it, I did buy a Sunrise FRED. All it is is the FRED, with two wires coming off of it. It needs a circuit board to work right.
I talked to the Richmond Controls guy; he had a bunch of different circuit applications to work with. I wanted one to fit in the back of an empty well car, which meant something flat and odd-shaped. He said he could do that, but he didn't have the parts at the show.
There's a guy on e-Bay that sells freight cars with built-in FREDs. His are powered by a couple of watch batteries; the circuit is glued to the B-end of the interior with the batteries on the roof. There is an on-off switch, which is attached to the brakewheel. Push on, Push off.
Dunno what model FRED he used, it is square in shape, and it is bright. The freight cars are either Blue Box Athearn or MDC Roundhouse.... I was going to ask him if he'd do a Athearn RTR or Genesis or some other brand of freight car, but haven't done so yet.
Kennedy