Help with kindergarten-level dynamo headlight troubleshooting
 

For my frankencommuter I have salvaged an old schwinn (prob. Union) bottle dynamo lightset with head and taillight.

Let's say that I want to make this work, regardless of how not awesome some readers might think it is.

Upon being pressed into service for the first time in 30 years, the taillight lit up brilliantly, but the headlight did not come on.

There is a single wire running from the dynamo to the front light. The socket appears to be designed so that the wire slips into the plastic socket and makes contact with the the threaded silvery cap on the bulb. When the bulb is inserted into the socket, the contact at the end of the bulb touches a contact at the far end of the socket, which I assume goes to ground in the bracket, which is attached to the stem.

I have tried replacing the wire with a new piece of wire with freshly stripped leads.

I have inspected the bulb, and the filament appears to be intact. I also tested with another bulb of the same type (also probably 30 years old, but bulb appears to be intact. Neither did this bulb work.

Should there be a ground wire coming from somewhere and going to somewhere?

What else might be wrong?

Thanks for any help you can provide.

Eric

Edit: I also made sure that the positive lead is not touching the ground contact in the socket.

Do you have a MultiMeter for checking voltage/resistance ,etc ? If not ,Harbor Freight has cheap ones that work well for under $10.

Ive had light bulbs & fuses that appeard to be good that didnt work.

Can you hold the bulb in your fingers,& take the wire that goes to the headlamp and hold it against the thread on the bulb and touch the other contact against bare metal on the frame to see if it lights ?

Good luck, dave

Thanks for your reply!!

I do have a meter, though it would take me a while to figure out how to use it.

Using a known good flashlight bulb, I have checked the wire I'm using with a couple of D batteries. Good. (it's old wire, but no hidden breaks inside the housing)

Using same wire and same batteries, I have checked the bulb. It lights up.

Bulb and wire are good.

Also, testing without the taillight inline, just in case that could make a difference.

For some reason, when I install the good wire from the dynamo to the front light, using the good bulb, and run the wheel so that the dynamo goes, the bulb will not light. Doesn't matter if I'm touching the ground of the bulb to the chromed steel light bracket or have it actually installed in the socket. (I also reached inside the socket with a tiny screwdriver and pried the ground contact forward a little to make sure it was contacting the bulb.)

I'm running out of ideas. This can't be that complicated.

Use the continuity-testing feature of your multimeter to check the continuity of the headlight/bulb/wire assembly and begin narrowing down where the connection problem lies. Also, don't run the taillight by itself or you'll nuke the taillight bulb and have to shop for one.

If the entire headlight/bulb/wire assembly has continuity, next check for continuity between the headlight bracket and the generator bracket. If they're not connected, you may need a dedicated ground wire between them, or at least between the frame and fork. I assume your generator's ground screw is present and is penetrating the frame's paint to the metal.

"A child of five would understand this. Send someone to fetch a child of five." -Groucho Marx ;)

I bet this is it. Weird thing is the taillight runs just fine on its own, and there's no ground screw in place. But perhaps the gen bracket is contacting some, ahem, iron oxide instead of paint where I can't see.

That was it! Thanks, guys!!