Mystery Parts in Taillight Assy

Larry,

Based on what I have read here on PC, the parts you are referring to control the LED's in the top of the light assembly. Most folks would call it the "brake" light. On the Gen II, the brake light is LED. IIRC, there is a circuit board that does control it.

I am impressed that you are recycling the way you are. Most folks would simply drop it in a trash can and forget about it.

I note you are new to the forum. "Welcome" to Prius Chat!

Ron

 

LEDs need to have resistors wired in series with them in order for them to work. Prius taillights have the resistors on a circuit board on the bottom and the LEDs at the top with your mystery wires connecting them.

Avi

 

To clarify everything, the light assembly for the Gen II consists of two different types of light emitting sources.

Those are incandescent and LED.

The incandescent bulbs will be found in the following locations: tail light bulb, turn signal bulb, and back up bulb.

The LED's will be found at the top and they are used specifically for the brake lights only.

As AVI pointed out, the resistors, diodes and so forth are required to make the LED's work. There are numerous reports where some of the LED's have burned out which has caused quite a bit of grief for certain Prius owners. I am not aware of a easy simple solution to replace individual LED's in the Gen II brake light at this time.

There are also aftermarket bulbs which are LED that can be purchased to replace the incandescent bulbs.

Ron

 

Incase anyone is interested: LED's need a certain voltage to operate, but once that voltage is reaches, the current that runs through it will ramp up very quickly with every little bit of extra voltage. See the graph. So a red LED (color of the lines equals color of LED) will consume 10mA at 2 volts and almost 10 times more at 3 volts (it will probably have burnt out by then).


A resistor will prevent this from happening by limiting the current through the LED.


Example: 6 red LED's in series will run nicely of off 12V (2V per LED) and draw 10mA.
The Prius DC-DC converter kicks in and the supply voltage increases to 14.4V. Now each LED gets 2.4V so (see graph) about 30mA!!!
Three times more current and a greatly decreased life-expectancy!

Now we put three LED's in series and serieswire them with a resistor. We assume 2V per LED, so 6V for all LED's and use this assumption to work back through all calculations.
The resistor now has to remove (12V minus 6V for the LED's is) 6V. And we know the current when the LED's get 2V, which is 10mA.
From a well known formula (V=IxR) this reveals the resistor needs to be R=6V/10mA= 600 ohm.

Now the Prius converter again kicks in and delivers 14.4V.

What happens to the LED's now???

It's hard to work out exactly, but for an approximation we assume all extra voltage is absorbed through the resistor, then a higher current will run through it, and therefor this current will also run through the LED's. Reality is actually even better for the LED's than this approximation!
So instead of (12V - 6V=) 6V, we now have (14.4V-6V=) 8.4V over the resistor. Now the current will therefor be: I=8.4/600=14mA.

Without resistor, the converter switching ON resulted in a 200% bigger current!
With the resistor, it's only 40% more current.

Of course we first had 6 LED's running of off the same power that only ran 3 LED's in the second example. But since LED's use very little power and (provided they are used properly) live 'forever', this is not often seen as much of a dilemma.