I've got a steel-framed bike with incandescent lights, probably from the '70s. Unfortunately, despite all my efforts to get it working, the headlamp refuses to work.
- About six months ago, the thing worked for a bit, even with its ancient, yellowed wires and bottle dynamo from a different era, but then suddenly stopped.
- About a month ago, I replaced the ancient incandescent bulb with a new one and cleaned the whole thing inside and cleaned the ancient bottle dynamo but that didn't make a difference.
- This weekend, I replaced the wiring for both the front and back with new double wiring†.
- With the new wiring, the bottle dynamo is easily powering the old taillamp, so it seems that it's neither the old dynamo nor the new wiring which is the culprit.
In the photo you can see the way the thing works. When I screw on the top, I bend the metal connector plate forward a bit in order to be more sure that it actually does connect to the bulb.
What might be going on here? — I doubt it could be any kind of short due to the fact that the cabling is brand-new and that the dynamo lights up the taillamp just fine (it even lights up with only a slight turn of the pedals, so it seems to be generating a good amount of current).
The only electrics-specific tools I've got is one of those screwdrivers which has an LED which lights up if the head detects a current. However, I'm not exactly enthusiastic to buy even more stuff for this endeavour because I've already wasted such a large amount of time and money...
† The old wiring was a single, ungrounded wire and I actually don't know what to do with the new ground wire because there's no obvious attachment point for it, so the new wiring is still basically a single cable.