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Brake light Quad-Mod for 05-07 Legacy


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(Note: Wasn't sue if this fell under Performance or Maintennance how-tos, so mods feel free to move this)


So, I was looking at my tail lights after buying my Leggy and I wasn't happy with what I saw. There were four bulbs behind red lenses, but two of them were jsut for turn signals. Why weren't they yellow? Well, they weren't carrying their weight.


I'm a big fan of visible brake lights. They're essential to safety and with how many people seem to drive by sheer luck, I figure I can use all the help I can get. High contrast (Off to On instead of half-bright to full-bright) brake lights are also something I like to have at night. So all I have to do is get the upper pair to light up when the brakes are on and I'm happy. I jsut have to get the turn signals to turn on when the brakes are off, and turn off when the brakes are on. Should be a piece of cake. A couple relays and I'll be done.


Fast forward two months.


I finally came up with this:



Two relays per side and some fancy wiring. Unfortunately, there are a few problems.


First, this would be noisy as hell. Brakes *click*, turn signal *klak**klak**klak*, both *clickklak**klak**klak*.


Second, sharp-eyed folks will probably see that I'm severing the ground I need to trigger the DPDT relay.


And third, the DPDT relay wouldn't have had enough draw to stop hyperflash.


If I had implemented this, I'd likely have had a disco going on behind me. So, unhappy with my result, and knowing nothing about electronic components smaller than a relay, I contacted a friend of mine who does know all this stuff. For those on CentralOhioSubarus.com or DirtyImpreza.com he goes by Teslamaster. After outlining my goal and what little I had, I asked him to come up with a solution that I could piece together with an electronics store and a soldering iron. His reply made me hit my head against the wall:


So I was drawing up a circuit for you when I realized I already have something that does just what you want installed in my car right now. It's the converter for my trailer lights.


What made this worse is that I had the same box in my WRX for my race trailer. So early moral in this story: Don't get too focused on a particular solution to a problem that's been stumping you. Try to think of situations where what you want to accomplish might have already been done.


After stopping the blood flow from my forehead, I set out to get some parts:


Hopkins Trailer Wiring Kit (#48925)

2xDorman Fully Insulated Disconnects (#85461)

You can use the connectors of your choice. I like these because they are fully insulated and will let me undo this mod if I need to.


You will also want to get a pair of sockets and 25W automotive bulbs or a pair of resistors to mimic them. Info on the resistors will come later when I get a reply from Teslamaster. But the bulbs will be easy to get and work fine. The socket design doesn't matter. I got a pair of 1157 sockets, but you can also find sockets for 7440/7443 bulbs.


And finally, get some quick taps. Either the clamp type found in most autoparts stores or Posi-Taps which are my favorites.


You'll also want your usual collection of tools: screwdrivers, wire tool, and an 8mm wrench or pass-thru ratchet.


Ok, let's get started:


Clean out your trunk. I know you've been saving that half-deflated beachball and old magazines for an impromptu '80s party, but it's time to let go.



Now there is a plastic piece in the middle of the trunk lp by your legs. In it are three "christmas trees" that hold the front of it in place.


Pull these out. I had good luck by using the plastic piece itself. But you do risk damaging it that way. Once they are out, the piece pulls straight up, popping out of four spots along the top; they are white in this picture:



With that gone, we need to remove the hooks to either side of the trunk opening:


Turn them 90 degrees towards you:


Then pull back the fuzzy lining and you'll see a tap facing you.


Push it in with a flat bladed screwdriver. The tabs at top and bottom will pass through openings in the bracket that you aligned when you spun the hook.


With the hooks out of the way, you can pull back the lining to expose the wiring. (You can remove the assemblies entirely if you want, but I just worked with them in the car.)



The top bulb is the bulb we want to pull its weight. It'll have black (negative) and white (positive) wires coming out of it.



Snip both wires and cap them with the disconnects. I used males on the harness side and females on the bulb side. You can come up with your own scheme, but keep it simple.

Here is the bulb plugged back in after doing this. (This is just to show it. We'll be leaving the bulb disconnected.)



Now the car's prepped, let's get to the box.


The scragly wires to the right are car-side, the ribbon to the left if trailer-side. The documentation, while simple, is clear. The box itself is even labeled on the backside. But to cover the wires for those reading along:



White = Ground

Red = Stop

Yellow = Left Turn (driver's side)

Green = Right Turn (passenger's side)

Brown = Park/Tail



White = Ground

Yellow = Left Bulb

Green = Right Bulb

Brown = Marker/Tail


If you look at the lengths, you'll see that it was designed to be installed on the left side of the car. Time to prep the wires. We don't have any use for the brown wires. The tails aren't changing. But the other wires do interest us.


Time to prep the car-side wires. Get your new bulb socket and if it's a dual filament socket like the one I have, find the bright-side positive so the high-load filament is hooked up. Twist the yellow wire with the positive from the new socket and cap it with a female end. Then cap the negative from the socket with another female end. Do the same with the other socket you bought and the green wire. If you were to plug it in at this point, it'd look like this on the driver's side:


(This picture was taken at the end of assembly, so everything is hooked up, we'll be retuning to this pic later.)

The reason why we're installing a new bulb here is because when the brakes are on, the trailer box uses the signal from the turn signal to turn OFF the bulb, not on. So the flasher thinks the bulb is burnt out. It works fine when the signal is on by itself. But will hyperflash if the brakes are on. It's possible, depending on how it's made, that an LED flasher wouldn't have this problem. But I didn't want to waste the money or time to find out. Putting bulbs BACK into the old positions (wiring-wise) was a sure-thing and could be done immediately.


Now on to the trailer-side wires. Cut the plug off the end and peel the wires apart from each other like a Twizzler Pull-N-Peel. :D It should look like this:



Now cut the trailer-side green wire and trailer-side white wire to the same length as the car-side green (if you need to). Cap them with male ends.


Trim the trailer-side yellow to match the car-side yellow. Cap with a male end.


Now take a length of wire (preferably white) about as long as the yellow wire you just trimmed and splice it into the trailer-side white wire. Cap this with a male end also.


Ok, so we have a loose collection of wires with carious ends and two bulbs, looking like some sort of alien macrophage. We can start hooking everything up.


(Continuing in next post)

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First, the ground. Take your 8mm wrench and remove the nut at the top of the driver's side taillight assembly. Slip the eyelet on the end of car-side white wire over the stud and replace the nut. It's good if the eyelet spins again as it need to bite into the metal a little for a good ground.



Next, the bottom bulb in the assembly is the brake bulb. It has black, red, and white w/ stripe wires. Contrary to what would make sense the striped white wire, NOT the red wire is the brake filament. The red wire is just the taillight. Splice the car-side red wire into this striped white wire. You can see it in this picture again:



Plug the yellow car-side wire into the white wire on the harness that used to go to the turn signal bulb. Then plug the socket's ground into the matching black. (Once again, see the pic above) Do the same with the green car-side wire and socket ground on the right side of the car.


Finally, plug the yellow trailer-side wire into the white wire coming from the old turn-signal bulb and the short trailer-side white wire into the corresponding black. Do the same on the other side with the trailer-side green into the white and long trailer-side white into the black.


Now test your Quad-Mod. It should work like this:

[ame=http://www.youtube.com/watch?v=pqld4ecazBI]Brake light Quad-Mod[/ame]


If everything works, clean up your wire routing, mount the trailer box, and stuff the new extra bulbs in amongst the wires. Be careful not to let the bulbs knock against the metal of the car or they might break and cause a short. They shouldn't cause any heat problems because they will only ever flash, so they won't get too hot. Just don't sit with your signals or hazards on for a long time to be on the safe side.


Remember when putting the hooks back in to push them in horizontal just like you pulled them out, then rotate them back down.


Fix your weatherstrip!




Full-size (GIGANTIC) versions of the pictures are available on my Flickr site in the Project Pics set.

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me like...


but not to be a jackass...but your concerned about safety AND you tinted your taillights?


True, got me there. I'm not a fan of tinted tails, but I hated all the chrome and "knurled" lensing more. That was another reason why I wanted to increase the light output. If I'm feeling froggy some day, I might cut strips out between the knurled lines in the outer lens.


So far it's looking bad for the resistor... But we haven't given up yet. As it is, the extra bulb trick works.

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Well, as above, you can do this mod and just have an extra bulb in amongst the wiring. No problems there. The proper resistor to use for this application is a big one that would have to use the metal of the body as a heat sink. So I'm going to get an LED flasher and see if that will solve the issue. Again, this mod works perfectly fine as described above. Go ahead and give it a go. You can always add the LED flasher later if it looks like it'll work.
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