The Brake Light Switch controls when your brake lights come on or off. When you start pressing the brake pedal, there is a small plunger that is somewhere close to the rod of the brake pedal. Depending on the design, when you press the brake pedal, the plunger either goes in or out, allowing a flow of electricity to your brake lights, turning them on. You step off the brake, plunger goes back in place, no more circuit, no more brake lights.
Old and new Brake Light Switch.
On my 1996 LS400, the plunger comes out as you push the pedal down. This design makes the most sense so I have a feeling most cars will be like that. When the brake is not depressed, that plunger you see in the above picture (reddish piece at the top) is pushed all the way in. As you press the brake pedal, it starts coming out, allowing electricity to light up the brake lights. Think of it as a cut-off switch. When the lights aren't needed, the circuit is blocked. As soon as you start pressing the brake pedal, the switch (plunger) opens the circuit to light up the lights.
Now that I described the same thing in three different ways, let's get to how to change it out.
I would recommend disconnecting the negative battery terminal whenever you work on electrical components. This job is very easy. However the tight space makes it a lot harder than it could be. If you're a big guy, you can do it but man, you're gonna be cursing.
Right below your cluster, in an LS400, is a black cover (well, it's black in my car). The OBDII port is actually connected to it. What you need to do is take the two screws out and let it hang. This will give you enough room to work. You don't have to take it all the way out.
There's a screw on the left and one on the right. These are the only two you have to take out. It will let your cover hang. When you get the screws out, the cover actually has two clips.
The first clip is right there. Put a screwdriver in between and carefully push the cover down using the screwdriver. It should pop out very easily. Do the same thing about four inches over.
When you go to reinstall this piece, you put the clips in first and it lines it up for the screws.
Next you need to locate the actual Brake Light Switch. It's high up in there right next to the brake pedal rod that goes up into the firewall. Initially I was having a hard time but once you find it, it's obvious. I believe part of it is blue, OEM or not.
This picture above actually shows the new Brake Light Switch installed in the old one's spot. I want to give you guys a better idea of where it is.
Now, removing the old one and putting the new one in is probably easier than messing around on your back in a tight location with a plastic cover hitting you in the head. I digress.
Look at the picture above again. You will see that there is two nuts. One is actually on the switch while one is mounted to the Brake Light Switch mount. Don't touch that one. You need to loosen the nut closest to the sensor.
Plastic cover removed.
What you also need to do before that is mark where the bolt was on the original switch. You need to line up the new one the same way. I used a marker and just stuck it in between the nut and the switch.
Moving on, disconnect the electrical connector. It has a little thing you push in and it comes right out. Then take a 14mm wrench (I don't see how you can use a socket) and just loosen the nut on the switch. About one full turn. At this point, you should be able to turn the whole sensor with your hand - unscrew it completely like that.
Tip: To initially get a wrench on that nut, you might need to press the brake pedal all the way down.
Put your switches side to side. The body of them might be different but the bolt and plunger should be the same. Now remember how I said you should mark where the nut was? It's so you know where the nut on your new switch should go. Honestly, I did it by eye and just made sure it goes in and out by pressing the pedal with my foot.
All you're gonna do is set that nut to the proper location on your new switch and screw that in with your hands. When the nut hits the mount, tighten it. Before you do so, press the brake pedal in and out a couple times to make sure that:
The plunger isn't so far in towards the firewall that it's pressing up against the little plate that releases the plunger. The plunger should be fully in when the brake is not pressed down and it should also start moving as soon as you start pressing the brake pedal (sometimes the pedal will have a little play in it - don't worry if the shaft doesn't even move until you press it like half an inch).
Obvious, really. Play with the pedal before you start working on it to see how it all works. Also like I said, I eyed the distance of my nut and it works fine.
Make sure you remember to plug the electrical connector into the Brake Light Switch before you put the cover back. I forgot and put it back and was left to wonder what is wrong for about two minutes before I realized.
Go ahead and connect your battery. If you followed the steps correctly - and it's not hard, anyone can do it and I encourage you to do so. You know the quote a shop gave me for that? $140. That's why I only go to a mechanic if it's my last resort.
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