Our lower level Christmas tree looked like something was missing, so I unearthed some postwar trains my dad had purchased in the 50s. Last year's loop featured a 736 from 1957, so I decided to get out a 2351 Milwaukee Road this year to pull the string of cars I put under the tree. Hooked up the mighty ZW, and ran a few loops with no problem. A drop of Mystery Oil here and there and everything was fine. I then decided to try out the horn - it worked the last time I had it out several years ago. Put in a fresh D cell and nothin' - I could hear the relay click up and down. Popped the hood again and made sure all the wiring was intact. Howeever, the battery bracket looked extremely dull, moreso than I remembered. I removed the screw hollding the relay to the bracket, then took the bracket off the frame. I got out a tube of Simichrome and rubbed a little on the battery/relay frame - nasty black gunk started coming off. What a difference - the bracket was shiny as a new nickel after some Simichrome action. I went all the way around and polished the entire bracket, then sprayed it down a few times with some CRC plastic compatible contact cleaner - the last of the black residue came off. Put everything back together and turned the chassis upside down - beeeeeeeeeeeeeeeeep!!!! Partial success - sometimes a diesel horn will work like that (flipping the chassis with a D cell in place causes the relay contact to close, completing the circuit). Back onto the track, put about 12 volts to the rails, hit the whistle control - beeeeeeeeeeeeeeeeeeeeeep! Sometimes scrubbing off decades of old tarnish and and gunk is all it takes to get a balky diesel horn back into form. 
I didn't use the Simichrome on the 2351 chassis - I don't know if it will take off the chemical blackening or not - I wouldn't suggest using it blackened or painted metal items. I only use Simichrome on unpainted/bare metal (great for bringing back aluminum AMT from the dull, gray tone to clean as a whistle, shiny aluminum sheen).
