I have a homemade bike trailer taillight interface that I designed in 1987, etched with FeCl and still working to this day, even in sub-zero temps. The circuit has 14 components, all original, and operates from a garden tractor battery carried in the trailer. The PCB is larger than a credit card, easily serviced and has traces of tarnish nowhere near the green coppertop roofs of Canada's Parliament buildings in Ottawa, Ontario.
No photos of this interface exist, only the circuit. It fit inside a Micronta 270-212 plastic case ( from the former Radio Shack in Canada, nka Source by Circuit City).