[Essex_29]

A super simple tip for finding electric shorts in a car.
A tip or a tool, you decide, but after using it once, I saved  the bulb and its leads and it became a tool.

This is great for finding problems in an electrical system.
Say, your parking light fuse blows. You try a new fuse, and as soon as you turn on the lights, it blows
again. That's where this simple tool comes in handy.
 
-Connect the bulb with two long wires to the fuse box, in place of the blown fuse.

- turn on the parking lights, and as you have a short, the bulb will illuminate. The
long leads will allow you to put the bulb where you can see it all the time.

- Now start looking for potential places where shorts can occure, remove bulbs, light
assemblies etcetera. If the H7 bulb dims or goes out, and the parking lamps light up,
you are close to finding the problem.
This is where this method for searching for an elecrical shortcut is so helpful, since you can
look for the problem and not be in any hurry, and you will instantly know when you find
 the issue.
If the circuit that is investigated draws more than 55 watts of power, the H7 bulb will not
go out when you move the bad wiring, or whatever is shorting, but it might dim and the
circuit might show signs of working, so you still have a good chance of finding the problem
without having to blow a dozen fuses.

I got the idea for this use of a bulb when the park fuse blew on my Caprice station wagon
and I had no idea for where to start looking.

Obviously you can use any bulb, 50-60 Watt driving light bulbs are ideal. You could repurpose
a sealed beam with a busted low. or an H4.

[Essex_29]

I used the H7 as a fuse when trying to activate all the nine relays and the fuse box I just wired.
All the relays worked, and since nothing was wired to any lights or other cusumers, the bulb just
lit up when I hit the starter. Of course the bulb lit up and nothing else happened, since the starter
 solenoid needs so much power that it just provided ground (negative) for the bulb.

[TFoch]

Great info!  Thanks

[sammons]

Nice!
I did something like that 40+ years ago with a sealed beam headlamp. Used a patch coard with alligator clips on both ends. Don't remember for what or how?? 

Had to butcher my coard on my 12v tube light yesterday for my speaker test. Out of all the miles of used speaker wire i have, (after changing to monster wire), i couldn't find any🙄  The lamp had a cigarete plug and alligator clips. I'll have to put that back together, handy light to have.