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Old 09-16-2015, 12:33 PM   #1 (permalink)
Daox's Avatar
Join Date: Dec 2007
Location: Germantown, WI
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CM400E - '81 Honda CM400E
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2nd gen Prius tail / brake light fix (LED)

I had the passenger brake light go out on my 2004 Prius a few weeks back. The brake light is comprised of a bunch of individual LED lights. I did some searching online and found out the 'fix' was just to replace the whole tail light assembly. Looking up prices, I found them for about $75 shipped. Not horrible, but I figured I'd take a crack at fixing it before plunking down the cash. I'll document the findings here.

First off, this is the (driver's side) tail light assembly. The black portion is the brake light, and each section you see has a normal 1/8" or so LED in it. This is the portion of the light that stopped working on mine.

So, I ripped mine out of the car. Its a fairly quick and painless procedure. This is the back side of the light once removed.

The foam piece is just held on with some adhesive backing, so I peeled it off. The yellow and black wire you see along the top of the assembly goes to the LED circuit board on the left side of the picture. From the LED circuit board, they go all the way to the right side of the picture to another circuit board that consists of a bunch of resistors and a diode.

The other circuit board is tucked away behind this white plastic piece.

Here we have the other circuit board. The resistors are all rated for 2W of power. The ones on the right are 20 ohm, the ones on the left are 9.1 ohm. At first I thought this was a voltage divider, but I'm now guessing its just limiting amperage to the LEDs. When I tested everything on this board it all appeared it be functioning properly. I didn't see any cracked solder joints either.

The next step is to get at the LED circuit board and see what the issue is. However, this is a bit more difficult as its inside the sealed tail light assembly. There is no access to it unless the rear lens cover is removed. I attempted to do this with the same procedure that headlights are disassembled, baking for a few minutes in the oven. This did not work at all. The glue didn't soften like the urethane headlight glue. I cracked the clear plastic in a few places before giving up. Also the time in the oven melted some of the black backing plastic. I had to take a heat gun and melt it back into place to reinstall the light for the time being. I now have a new tail light on order, but will continue this analysis once I get the new light installed.

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Current project: A better alternator delete
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