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Long time ago my wife used to say"maybe there is a short in the bulb" whenever a bulb was not working in someone's house and they couldn't find the problem

As an electrical contractor I dealt with a lot of situations where for a reason or another the bulb failed to work.
"There is never a short in the bulb" I explained to her,enumerating all other possibilities that cause a lighting circuit to fail.


As I explained in MY RED SCOOTER IS BLACK thread some kid stole my scooter. When I got it back I noticed the head lamp was not working.
Then I found the battery to be discharged.
I fully charged it but after starting the scooter a few times it would die. I measured the charging voltage with the battery removed and it was about half what it should be.
The problem, I thought, must be the alternator or rectifier (regulator) While running I measured the voltage of a wire which was supposed to be between 20V and 80v pending the RPM of the engine. It was 6V.
When I unplugged the alternator the voltage went up to 20 v while running. So I knew there is a short between alternator and rectifier.
I decided to play with all the switches while running and noted that with the switch in high beam position there was no short but with the low beam on the circuit was shorted. After checking the wire for a bit I decided to remove the bulb. Now regardless of the position of the switch there was no short.
I ran two wires straight from the battery and noticed that indeed the bulb was shorted on the low beam.I have changed the bulb and now the headlamp works and the battery is charging.
So after all these years my wife was right, there is such a thing as shorted bulb,
 

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Overheard in High School Electronics class back in the day... "Hey - I found the problem with this TV - THE FUSE IS SHORTED!" :D

Back when I had my Suzuki 550 I was on my way home from Silverthorne and the bike simply quit - dead as a doornail. I coasted to the side of the road, checked and found the main fuse blown. If I recall, that was the ONLY fuse on that bike. Put in a spare which immediately blew when I turned on the key. This bike had an OFF position on the headlight switch, so I switched it off and put in another fuse. Life again! So I rode home with the lights off.

Once home I began investigating this. The bike had one of the old-style Large round automotive sealed-beam headlights, the kind with the round slotted metal disk held in front of the two filaments to direct the high and low beam light.

This bulb the metal disk had broken loose and slid backward over the metal leads that hold the filament wires, all of this poking thru the slot in the metal disk, so the bulb was indeed shorted. I bet that's what happened in your scooter headlight.

That wasn't the only headlight failure I had in that bike (It was my "ride" for 20 years!), I had a Halogen type headlight in there (large sealed-beam headlight bulb with little quartz-halogen bulb inside it), going down the road at night and the headlight went out! Switched to high beam and it was dead, too. Pulled over and found the little quartz-halogen bulb inside the sealed beam had broken loose from its connections and was laying in the bottom of the sealed-beam bulb. Made my way back to the little town 2 miles behind me by the light of the turn-signal.

Fortunately this was back in the day where most cars had either four small round sealed beams or two large ones, or four or two rectangular sealed beams, and you could buy headlight bulbs in convenience stores. They only had to stock six different bulbs. So I was quickly on my way again. This isn't true anymore, there's an entire aisle in automotive stores now for all the different bulbs. Matter of fact, the old sealed-beams are getting kinda scarce!
 

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This bulb the metal disk had broken loose and slid backward over the metal leads that hold the filament wires, all of this poking thru the slot in the metal disk, so the bulb was indeed shorted. I bet that's what happened in your scooter headlight.
I had a 68 chevy pickup once upon a time that had that happen but what it did was short the 2 together so both high & low beam were on all the time. Had a hard time figuring out what was wrong, after I had replaced the dimmer switch.
 
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