Reversed LED wedge bulbs blow fuses - why?

eggsalad

Enlightened
Joined
Mar 30, 2013
Messages
268
Picked up a new-to-me 2008 Prius.

Map lights use a wedge-base bulb, 168, etc.

Of course when you put in an LED you have a 50/50 shot of getting the polarity right. If you get it wrong, just pull the bulb and 180 it.

When I got it wrong in my Chevy, it just didn't work. That makes sense, because an LED is a diode and if you reverse the polarity, it looks like an open circuit.

But when I got the polarity wrong in the Toyota, it popped the fuse. I can't make sense of that.

Can someone explain this to me?
 

Alaric Darconville

Flashlight Enthusiast
Joined
Sep 2, 2001
Messages
5,377
Location
Stillwater, America
But when I got the polarity wrong in the Toyota, it popped the fuse. I can't make sense of that.

Can someone explain this to me?

You could always find the polarity with a VOM. Resistance in the wrong direction should essentially look like an open.

What bulbs are you using? Are you sure you didn't short the hot to the body accidentally?
 

eggsalad

Enlightened
Joined
Mar 30, 2013
Messages
268
You could always find the polarity with a VOM. Resistance in the wrong direction should essentially look like an open.

Yup. That would have been the smart thing to do!


What bulbs are you using?

El Cheapo specials from my generally trustworthy favorite vendor.

Are you sure you didn't short the hot to the body accidentally?

No, that's not possible. The bulb socket was hanging in free air when it happened.
 

Alaric Darconville

Flashlight Enthusiast
Joined
Sep 2, 2001
Messages
5,377
Location
Stillwater, America
Yup. That would have been the smart thing to do!
What's that one thing that's 20/20?

El Cheapo specials from my generally trustworthy favorite vendor.
You don't get what you don't pay for.

No, that's not possible. The bulb socket was hanging in free air when it happened.
Weird. Must be a blocking diode that is easily overcome and does some kind of thermal runaway.
 

JasonOk

Newly Enlightened
Joined
Aug 31, 2017
Messages
66
Location
Oklahoma
Not a solution to your promblem but i'm running the 2886x bulbs in my wedge base interior with execellent resulst (my opion obviously)
 

jzchen

Enlightened
Joined
Jan 16, 2015
Messages
328
Location
Arcadia, CA
The question in my mind is does the bulb work now that you replaced the fuse? Maybe it was faulty in the "forward" direction and blew the fuse, in the correct orientation.
 

eggsalad

Enlightened
Joined
Mar 30, 2013
Messages
268
Unsolved mystery. The "bulb" that blew a fuse in socket A works fine in socket B, and another one works fine in socket A. We'll never know.
 
Top