LED THIRD BRAKE LIGHT
 

Thinking of making an "attention getting" third brake light. (Emphasis on ATTENTION GETTING, like bright enough to get the attention of the idiots on their phones rear ending people at traffic lights)

Something I can mount on the package tray or outside on the rear deck ON MY convertible - temporarily for driving and unplug / remove for show.

I got this 22" light bar with 40 LEDs (300w). I think I can make a red lens for it and mute it a bit if it's too bright.

What's the best way to hook it up? can I tap it into the brake lights circuit? Should I run a separate line & second brake switch?

Thoughts?

I'd run a separate wire to the existing brake light switch.
If you really want to get the attention of that tailgater behind you add one of these strobe flashers to the third brake light. http://www.ebay.com/itm/121607090542

They flash 3 times per second when the brake is intialy applied, then 3 times in 3 seconds then it stays on until the brake is released. I bought one to put on one of my trailers but haven't installed it yet.

300 watts at 12 volts is 25 amps, a bit much to run through the brake light switch along with the current your regular brake lamps are pulling. I'd use a relay like this:

Nice! Thanks. I like the strobe too!

What you are proposing for stop lights is equal to off road search lights. Running these on the road may get you a moving violation. A 1057 regular incandescent bulb for a stop light is about 27 watts. You looking at 10 times that plus leds are 8 times brighter watt for watt. Check out well, before installing.

Yes I figure way too bright as is, but I think I should be able to dial it back with the right thickness / density of red lens. I want to push it to the limit but not beyond. How does one determine where the limit is?

I've seen some pretty annoyingly bright LED's on some new cars (a Cadillac comes to mind)... that's the brightness I'm looking for (and lots of it)... Also wondering if something like a micro switch under the dash to just flick it when I think somebody behind is coming up too fast.... or a switch to activate/deactivate the thing based on driver's decision... not some computer...

It has also occurred to me that as more cars adopt accident avoidance 'features' on their cars, pretty soon we may be able to thread our vintage iron through traffic like we're on an empty highway, because all the smart cars will look out for us and be getting out of our way. ;)