Here's a new one.

I have an 83 650 Nighthawk in the shop. Among other issues the owner wanted me to fix the brake light - said it didn't come on with either brake.

When I powered it up it looked like the brake light was on. I disconnected both brake switches and it still looked like it was on.

Pulled the socket out and sure enough both filaments were lit. I thought maybe it was a bad ground but ground checked ok.

The system was acting like the bulb had an internal short between the filaments. Testing the bulb base showed a circuit to only one filament. As I finished doing that I noticed something didn't look right.

Turns out the brake filament had broken off at the end, swung across the gap, and welded itself to the end of the tail light filament.

Who'd a thunk? Wanted to share in case anyone else ever runs across this.

 

Now that's what you call a hidden electrical problem! Nice work!

 

Would that now be an 1156.5 bulb then?

 

wow!!! every other lighting fixture gets old and dies and you found the one that gets old and brighter!!!??? nice work!!

Shaun

 

Happens in older cars that uses the double filament too.

 

Wow, that's insane. I work in an automotive shop so I've seen plenty of bulbs that look blows but have re-welded themselves back together but never one that completes a completely different circuit. Sit down and take a break, I think you just earned a cookie, lol.

 

HA.. I've seen that a couple of times and everyone looks at me like I'm crazy when I tell them how i had to fix their bulb to get all the marker lights to stop comming on when they hit the brakes(semi trailers)
or turns.

 

It happens more than you think.
We had a semi trailer at work that had an electrical issue, and that ended up being the problem. After working on the lights for hours, the mechanic was stumped on what was wrong with the lights. I told him about lights burning out and bulbs doing funny things sometimes (filements welding together, etc.) and he finally found the problem. One little bulb had burned out and did just what you mentioned. The filiments welded together making one curcuit, which screwed up all the lights on the trailer.
It's funny how just one small bulb can screw up the whole project.
First thing to look at when having light issues is to remove all the bulbs an start re-installing them one at a time to find the bad one. Lesson learned.