SOLVED: Partial brake lights stuck on issue

SOLVED TLDR: Wires were swapped in the taillight portion of the wiring harness. After swapping them with the help of all below, brake lights work properly.


I’ve got a weird problem with my truck, and it’s been this way since I bought it. Being where they’re at, I didn’t realize it until my wife was following me one night. The main brake lights are always on when my headlights are on. Not the third brake light on the cab, just the two tail light portions.

I tested it visually again just now to verify, and it’s as follows:

Headlight switch off: nothing; press brake pedal, and brake lights turn on.
Same with switch in DRL.

Headlight switch in marker/on position: brake lights stay on with what I assume is double the brightness of the daytime brake lights, but as stated above, only the tail light portion.

I google searched for similar issues but found all brake lights or nothing. Anyone had this problem before? I’d like to think it’s a relay issue or something easy, but figured I’d ask before I went crazy chasing something I don’t know.

Thanks in advance!

 

You could check if someone stuck the wrong bulbs in there. While you have the tail lights out, look if there’s something fishy with the wires. Cut & spliced together wrong or something. Check if power is getting to the bulb sockets correctly. Probably 3 wires. 1 ground, 1 gets running lights power, 1 gets power when the brake pedal is pressed.

 

This is a strange case for sure.
Let’s get any aftermarket stuff out of the way.
Do you have any after market accessories.

Do you have a towing harness?
If so, is it OEM?

 

I’m planning on pulling them tomorrow to see if that might be the case. I was crawling around tonight underneath to see if there were any stray wires near the area, as I had wondered if the previous owner tapped power out of the brake lights for the bumper lights, but it doesn’t appear that that’s the case.

There are aftermarket lights in the Pelfreybilt bumper, which is what I wonder if the previous owner had tapped, but initially looking at it without pulling the taillights didn’t make it appear that way. As mentioned above to Washeem, I’m going to pull them tomorrow and see if maybe that’s the case.

I do have a towing harness, judging by the broken plastic portion it is OEM . It had been tucked away and bagged by the previous owner also, but it’s not damaged in a way that looks like it’d be shorting anything. I kinda thought about that too after reading similar threads, but figured if it was shorting they’d be stuck on with the switch off also.

 

It sounds like your tail lights are the problem.
Since it does it in the Parking/Marker Light position.

What has me thrown is, that the Center High Mount Light (on the cab) does NOT have this problem, correct?

 

Yep. That’s the weird part. It functions completely normal, and has been the biggest reason I haven’t made a bigger deal out of it.

It’s finally just got to a point where I’m thinking “I should probably figure that out.”

 

Another thing to check is the ground. I had a car the left turn signal wouldn’t flash, just stayed lit. Once I got a good ground it worked. But it’s strange both sides has this issue on yours.

 

Don't know if this has been stated already but according to your bio info you have a 2007, the LED tail lights weren't added or standard until 2009 so I suspect the previous owner tried to install the LED tails on your truck which is intended to have the incandescent tails and something is wired improperly at the tail light to main body wiring harness connection.

Edit: never mind I confuse somebody else for OP.

 

This would be my first guess as well. Something is switched around. It's like it's functioning appropriately, just energizing the wrong set of lights.

 

I don't think you have a problem, if the headlights are in the ON position then something should be glowing at the rear taillights. When you press the brakes the 3rd brake light comes on and the LED taillights glow brighter.

When the headlights are turned on do you have license plate illumination lights? There should be little red parking lights on the upper side of each taillight housing, do those come on?

 

I’ll take a look at it all this morning, thanks for the ideas!

I got confused for a second there too .

b_r_o pointed out something else I had missed below, so there’s definitely something going on.

They don’t get any brighter though, which is the issue, they stay at the maximum brightness when the pedal is pressed.

removed the next bit cause I’m an early morning idiot and was thinking about the turn signals

 

Sounds to me like the taillight and brake light wires for the taillight assemblies are swapped. To test this theory, apply the brakes with the headlights off and observe the taillight brightness. Now turn on the headlights in addition to the brake lights. If the taillights got brighter when you turned on the headlights, that's your problem.

 

I think I mentioned that above, but just to make sure:

Headlights off: no taillight and brakes light up when pedal pressed.

Headlights on: brakes stay on and don’t get any brighter when pressed.

So I guess that makes sense. Now I just have to figure out which of those wires to switch.

 

So the little bit of organizer in me wants to say this is wrong, and where my problem lies, as I would expect most of these color coded wires to go to the same color. Any of this look wrong or familiar?

(Bearing in mind, it is unplugged as I removed the zip tie to do so).

 

I know this has not been mentioned but you may have a faulty brake switch. Being that you are the newest of the 2nd gens you'd be surprised how much Toyota cheaped the heck out on parts quality.

In these situations it is absolutely imperative that you have A. Schematics handy, or at least access to, and B. A power probe or access to.

 

I would’ve thought that also if it weren’t for the third brake light functioning normally. . .

 

That is irrelevant when you're talking electrical. Electrical tends to fail in the weirdest of ways. It can still be shorting in such an odd way where it activates two but leaves the third off until depressed.

 

Think it would do it in a way where it functions normally with the headlight switch off, then not function with it on though? That seems like a lot of right for just one wrong function. . .

 

You'd be surprised how vital the brake switch is, factor in CAN communication, and it can wreak havoc when it is not functioning properly.

It's worth a check.

 

The red and green wire, to the middle bulb socket. The little black thing those 2 wires go through, did you pull it out or was it like that already? The little black thing helps keep water out, and may need to be in place to help keep the wires separated. Look in there, the 2 wires may be touching. But strange it would affect both sides.

Since you're this far, you have a multimeter? Black should be ground, check that, .7 ohm or less should be good. The red and green are for brake and running lights, not in that order. Hook negative lead to ground, probe red, step on the brake pedal, power? Step on the brake pedal, probe green wire, power? Next do the same but turn on the headlights, red power? Green power?

Boggles my mind why they would change wire colors after a connector. It really pisses me off when the wire color changes inside a harness.