Bottle dynamo wiring a headlight and taillight on 1980s bike I'm restoring a 1980 DBS Winner bicycle, and I'm having trouble wiring the dynamo to the headlight and taillight. As a disclaimer, I know very little about electricity and wiring. 

The dynamo has two outputs on the bottom, one is labeled S and the other is labeled B. There's a wire between the S and the headlight. From B, however, a wire goes directly to the frame itself (screwed-ish to the head tube). Below the crank is a similar screw-ish contraption, from which a wire goes to the taillight. I'm thinking the current is lead between these contraptions, via the steel frame. 

None of the lights work when the dynamo is on. I tested the bulbs with a battery, they work. I've tested the dynamo output with a voltmeter, and it seems to work. I also tried connecting the wire from B to the side of the bulb in the headlight and the wire from S to the bottom of the bulb, which worked when the dynamo was on. Do both the taillight and the headlight need two wires each? I find it strange if that is the case, since the bike came with one wire to each light, and it's weird to remove only one wire from each for whatever reason, isn't it?

Update: Added some images.
@Plasma says: I got it working! You're right @Carel, the frame itself wasn't negative, but the back fender somehow was. I didn't check if the entire frame was positive, though, so can't say anyrhing about insulated wires or not. Anyhow, the problem seems to have been a missing connection between the positive and the taillight bulb. I DIYed a new socket for the bulb and did some (possibly redundant) new wiring to connect everything properly.

(because I don't like unanswered questions)