school me about diodes

I just read Mart's post, and he has a point with the stop/flasher lights combined the diode isn't a solution. Maybe I just won't use the 3rd light. Thank you Mart.
 
40cpe said:
I want to install a 3rd brake light without going all the way up to the brake light switch for power by installing a diode in a wire from each brake light socket feed. I see many different names for the diodes and am confused as to which type I need. What kind/size/rating of diode do I use for this purpose? My system is 12 volts.
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I understand your wish to make connections strictly in the trunk. Two power diodes such as the 1N5400 will pass 3 amps and reject 50 volts may do what you want and they are cheap. Use 2 diodes to gather brake and turn signals voltage to yield these results = When you turn on your turn signal on flashing the brake lights on one side, the 3rd brake light will also flash. When you brake to turn and the brake light comes on solid on the other side, the 3rd brake light will quit blinking but will go on solidly If this is ok, (positive ground car>) connect the anode of each diode to the 3rd brake light and individual cathodes to each brake light. (negative ground car>) connect the individual anodes to each brake light and connect cathodes together at the 3rd brake light.

Diodes, yes many exist but you are switching power so you would use power diodes. Diode function ... a wire passes electricity regardless of which way you face the wire. Diodes pass electricity only one direction. The anode must be more positive than the cathode. Electrically characteristics are basically how much current will flow and how much voltage it will keep from flowing.

Back to the 3rd light...I am going to use a separate mechanical brake switch and a 3rdbrakeflasher.com which rapidly flashs the brake signal before going solid. $15-$20. G-Force units are $30 sensing how urgently you are stopping and changing the flashing accordingly.

Also, modules are available to separate the turn signals from the brake light signals so the 3rd light gets brakes only. Connect to each brake light.

Also, a module may do what you want but I haven't used ::: click for link Claims to filter the turn signal out of the third brake light This may be the answer to using 2 diodes.
 
The turn signal switch is what separates the turn signal circuit from the brake light circuit. When one side flashes the other side is isolated for the brake light function and vice versa. I'm not sure how a diode will help you there. If you tie them together with two diodes then is will still blink until the brake light comes on. If you only use feed from one side with a diode, it will blink when that side is selected with no circuit path for a brake light but work OK when the other side is selected.

Using the brake light switch feed before the turn signal switch is the only way I can see that it will work a third lamp with no turn signal feedback. A brake logic module might do the separation but I have no experience with them.
 
40 CPE .....Just to clarify....Below is a table showing all the possible L & R signal light conditions, and the desired output for the 3rd light. Is this what you expect to happen?
CONDITION L R 3RD
_____________________________________

1-no turn, no brakes off off off
2-no turn, brakes on on on on
3-left turn, no brakes flash off off
4-left turn, brakes on flash on on
5-right turn, no brakes off flash off
6-right turn, brakes on on flash on

Al
 
40 CPE .....Below is a table showing all the possible L & R signal light conditions, and the desired output for the 3rd light. Is this what you expect to happen?

CONDITION L R 3RD
---------------------------------------------------------
1-no turn, no brakes off off off
2-no turn, brakes on on on on
3-left turn, no brakes flash off off
4-left turn, brakes on flash on on
5-right turn, no brakes off flash off
6-right turn, brakes on on flash on

Al
 
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Still didn't work !!!! The last three words in each line correspond to the L,R and 3rd light states correspondingly . So for condition 5 for instance L should be off, R should be flashing and 3rd should be off
 
Looking up info on the brake light logic modules shows them to be what is needed when wiring in from the rear of the car. They don't mention what voltage they work on though. I just have to assume they are for 12-volt systems. None of them want to tell you much about their products.
 
I can get you closer if you can,t get under car.
The power to signal light switch is from the brake light switch,at colum splice that wire before the smart signal switch and run to 3rd light.Keep it simple.
 
If you can spend time under the car, consider adding an additional switch on the brake arm. A mechanical switch will come on sooner than the stock hydraulic switch, warning texters behind you 20-30 feet sooner. After all that is the purpose of the 3rd light so consider doing it up proper. A mechanical brake switch is on my list. I already have a window mount 3rd light for the rear window and the led's work nice on 6v and the flasher for it..
 
Why not take a course in basic electronic. It will help you in a lot on the car and working around the house.
 
I installed the "Brakelighter" third brake light on my 37 that has turn signals and brake lights on the same circuit. The light is LED, 12 inches long, split down the middle for left and right illumination. You connect three small gauge wires (in the trunk if you want). One for the left brake/turn, one for the right brake/turn, and one to ground. When you hit the brakes, both sides of the third light illuminate. When you active either turn signal, that side of the light will flash and the opposite side will illuminate steady. So, not only do you get a third brake, you also get left and right turn signals. It mounts on the inside of the back window, where it is much more visible up high. It is very bright. But, it does cost about 55 bucks. It comes in either 6 or 12 volt. www.brakelighter.com
 
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