Fused Headlight

Apr 27, 2024

New puzzler time. 

Okay, here we go.

This happened years ago in the middle of winter. 

My neighbor Frank asked me to take his jalopy in for some repairs. His old Lincoln. He made a list of things he wanted done. He wanted a tune up, an oil change and check the brakes and put new belts on and replace the leaking valve cover gaskets. All the things you do. 

And being neighbors, he didn't bring the car into the garage. He actually asked me to drive it in myself. So I did. And I did all the things on his car at the garage. Then that night, I am driving the car home to his house. 

So while I was driving the car home, I stopped at a traffic light and I noticed something interesting.  There was a light shining under the dashboard. In fact, it was lighting up my feet. And I thought it was interesting. It seemed like a courtesy cabin light or something. 

So, I keep driving home because I know my wife is making this amazing, well thought out dinner, and I don't want to miss it. But I also want to know where this light is coming from. So, as I am driving, I lean down to try to glance under the dashboard. (Don't try this at home please!)

So what I see under the dashboard is in fact a headlight. A headlight that is somehow wired into the fuse box, under the dashboard of the car. I didn't notice it during the day, of course. But that night, it became clear there was a headlight under there. 

So, I get home and I deliver the car to Frank. And when I get there, I hand over the keys and hand him the bill. And then I said, "Oh, by the way, I think there was something you wanted fixed that you forgot to tell me about, right?"

And he said, "Oh yes, you're right!"

So, what was the light doing under the dashboard? What was the purpose of the headlight that was wired into the fuse box under the dashboard?

Good luck.
 

Answer: 

So, what was the purpose of the headlight that was wired into the fuse box under the dashboard of my neighbors old car?

What did he forget to ask me to fix?

What he had failed to ask me to fix was a short circuit, an intermittent short circuit that the car had. Every once in a while his brake lights would fail because the fuse would blow out. But he wouldn't know that the fuse had blown until someone would pull up next to him and tell him that his brake lights were out. 

So what he did was he wired a headlight in parallel with the fuse. So when the fuse would blow, the headlight under the dash would light up, because the current would go through the headlight, instead of the fuse. The headlight and the fuse have very different resistance levels. So, as soon as the fuse would blow, the light under the dash would come on, and he would know his brake lights were out. 

Good one. 


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