Thanks for your reply, and all the information! But please consider this: Let's say I wire the lamps without a bridge rectifier, so the wire goes to the positive terminal of the headlight and the ground goes to the positive terminal of the tail light; then the AC current would alternate between the head and the tail lights. There would be a flickering effect at low speed (bicycle dynamo lights always flicker, but this would flick more). Would it work? Would it damage the LED's?
There will be flickering at slow speeds but the serious problem this will cause is the reverse current when the AC wave is going negative. These LED's may not tolerate any reverse voltage. The diodes used in a rectifier are made to block high voltage so no damage is done. An LED is made to emit light when passing current and is not made for blocking current. If you force it to block reverse current additional heat will be generated which will burn out the LED. You can purchase them as a single component. Radio Shack has a suitable bridge rectifier that will work fine except it will not be as efficient as using four 1n5818 diodes. The part number is 276-1152.
http://www.radioshack.com/sm-1-4a-10...i-2062581.html
Only one wire is marked with a + sign. This is the wire that will connect to the positive (+) lead of an LED. The wire opposite the + marked wire is the negative lead and connects to the negative (-) lead of the LED. The other two wires are connected to the dynamo and it makes no difference which one is connected to the dynamo output terminal. The other wire will connect to the bicycle frame as the dynamo uses a frame ground for the other connection. This requires you keep both positive and negative DC wires isolated from the bicycle frame. This will cause a problem when trying to use an LED replacement bulb in a dynamo light. The fix for this problem is to mount the headlight to the bike with a plastic clamp so the headlight is isolated from the bicycle frame. After you do this all you do is run the negative wire from the rectifier to the isolated mounting bracket on the light.