George,
I believe that the tender bells for the postwar 1656 family, and prewar 227 (8976) family and 203 family are all wired the same. The drawing below shows the bell wiring. It also includes a little of the details of the teledyne and Magic electrol, which were prewar features. This drawing is from the TCA Bulliten magazine, which is available on line if you are a TCA member. It is from many years ago, but I do not recall the date. I believe they are indexed.
The wiring is not as you described. The heater for the bi metallic strip is energized continuously. The bell and heater get power from the lamp base on the underside of the lamp plate. The heater is grounded on the lamp plate, the bell is grounded thru the switch to the tender frame. You may have two wires that run from the tender to the locomotive. One of those is a ground wire. The four wheel loco has trouble keeping contact thru switches. The other wire goes from the accessory shoe on the tender truck to the front coupler. When the coil coupler on the tender truck is energized, the front coupler on the locomotive is also energized thru this wire.
I have seen warnings that some of the bi matilic strip heaters were in series with the back up lamp and use of the wrong lamp could result in overheating the nichrome wire. But I can not recall ever seeing one wired like that.
I do not want to take a tender apart to photograph it. As I recall to see the under side of the lamp plate requires removing the lamp plate support bracket, which requires removing the rear truck, which requires unsoldering the front coupler wire. I will see if I can find a spare part and photograph that. It will probably be a prewar part, but I think they are the same.
