Headunit dimming (night mode) when pressing brakes.

Any idea why my headunit dims briefly when stepping on the brakes? It'll flicker into night mode on broad daylight when doing so.

It only happens with the brake lights activating or active.

 

Aftermarket or stock?

 

Both.

If I'm in Android auto it'll briefly go into and out of dark mode when I press the brakes. If I'm not in Android auto, the LED capacitive buttons will dim and lighten repeatedly.

Put in my stock one and the same happens with it triggering as if the headlights were activated, but I know the headlights are off as they don't flicker on when this happens.

 

How old is your battery?

 

Came with the truck. Probably 2 years?

 

Who installed the aftermarket HU?
Does it still dim down when you turn the parking/headlights on?

 

I did. No splicing wires, just tundra specific harnesses. It properly switches to night mode with the parking lights or headlights on.

 

I’m thinking a poor ground connection to one of the tail light assemblies, or corrosion inside the trailer socket.


Stock tail lights? Any LED bulbs?

 

Stock. I'm going to look into the tail light harnesses then.

 

Went through all the brake light bulbs and connections, and nothing seems out of place. Reseated the bulbs, made sure all connections were solid, but nothing seems to change the flickering back and forth on night mode on my head unit when I press that brakes. It's also random, but happens most of the time I'm braking.

 

I'm not super good with electronics so maybe someone smarter than me can comment but is it possible that when applying the brakes, it's causing a larger load on the electronics which causes them to dim?

Do a full load test on the battery to rule that out.

 

You know, I had considered that, and now that you mention it I can't remember if it happened when I installed the amp or not. I'm going to look into that.

 

Well, it's not the amp. I disconnected the amps, and the flickering still occurs most times I press the brakes. This is a real head scratcher.

I even tried to turn off HVAC, anything not needed to drive really.

Here's a video of the issue. It'll also flicker back and forth intermittently at stop lights while the brake is depressed. AC is on in this video.

https://imgur.com/Xr4iPyx

 

Do you have any kind of resistors wired in for any reason? Did you wire up any sort of bypass to be able to use functions while driving?

 

Bought the car used, but I don't see any resistors on the tail lights.

No bypass for functions to use with car off.

 

How do things look inside the trailer electrical socket? No corrosion or nastiness there?

 

Not to use with the car off, but to use all functions of the HU even if the parking brake isn't set.
I can't tell what brand your HU is.
Is there a parking brake bypass or something like this on the radio?

 

Also, read thru this thread.
He ended up having some crushed wires that were shorting out and blowing the fuse when he turned his lights on.

Blown tail light fuse | Toyota Tundra Forum (tundras.com)

Not sure what connection your brake circuit and your HU would have in common unless its a ground somewhere..

 

Something is wired wrong.
There is no connection to the HU and stop circuit, unless it is deep in the ground connections...


Couldn't find a connection in the ECU-IG No.1 or stop fuse to the radio either.

7.5A ECU-IG No.1
ABS
Auto LSD
Blind Spot Monitor System
Multiplex Communication System (CAN)
Parking Assist (Intuitive Parking Assist)
Power Tilt and Power Telescopic
Rear Window Defogger
Shift Lock (Column Shift)
Shift Lock (Floor Shift)
Stop Light
Theft Deterrent
Tire Pressure Warning System
TRAC
Trailer Towing
VSC

15A STOP
ABS
Auto LSD
Cruise Control (1GR-FE)
Cruise Control (1UR-FE)
Cruise Control (3UR-FE, 3UR-FBE)
Electronically Controlled Transmission and A/T Indicator (1GR-FE)
Electronically Controlled Transmission and A/T Indicator (1UR-FE)
Electronically Controlled Transmission and A/T Indicator (3UR-FE,
3UR-FBE)
Engine Control (1GR-FE)
Engine Control (1UR-FE)
Engine Control (3UR-FE, 3UR-FBE)
Shift Lock (Column Shift)
Shift Lock (Floor Shift)
Stop Light
TRAC
Trailer Towing
VSC

 

This same thing happened to me when I pulled power from the trailer plug wiring to run extra lights in the back. When I disconnected it. Everything went back to normal

 

The thing is this is just plugged into the factory harness with a supplied harness. Nothing was spliced.

 

So your head unit would dim randomly from this until you disconnected the wiring you tapped?

 

Something is triggering the darker illumination of the HU when you hit the brakes.
Is it the same action that takes place when you turn the parking/headlights on?
Does the screen turn dark, like the flash in the video, when you turn on the parking/headlights?

Did it ever work correctly without the dark flash when you hit the brakes?
Or did that start you installed the after-market HU?

Does it only do it when you are driving, or will the HU flash with the key on, the engine off, and you hit the brake pedal while parked?

The odd thing is in the 9 pages of the illumination circuit, the circuit makes all switches and stuff light up in the dash and triggers the HU darkening, there is no connection to the brake/stop light circuit.

 

Yes

 

Turning on the headlights or parking lights will set the screen to constant dark mode without flickering. In other words, proper dark mode stays in dark mode. It did work properly before as far as I know, but it's done this with the aftermarket HU it came with, the new one, and the stock one that was provided with the truck (prev owner installed the first aftermarket HU and gave me the stock one with the truck purchase).

I tried to get it to flicker when in park, but couldn't get it to happen. When I'm in neutral I can get it to flicker with the brakes.

I can get the HU to dark mode flicker with the headlight stalk set to either off or auto.

 

It seems like when you step on the brake, that circuit is shorting to the illumination circuit and triggering the HU as if the lights were on.
But it is odd that it only flickers.
It seems if that was the case, that the HU would STAY on dark mode as long as the brake light was on.

Sorry so many posts, it is bugging me we can't figure out what the issue is..

 

I actually appreciate your help on this. My thoughts initially were also a short, but it's really peculiar how it's only a flicker.

Battery load also makes sense, but again where and why is that an issue as well?

 

Battery issues can cause all sort of stuff you don't expect. Same with alternator. I had some corrosion on the wires going to my alternator on my land cruiser and it caused the door locks to constantly keep unlocking when i had my foot on the brake. And a bunch of my lights didn't work + HVAC was going haywire. Interesting that it happens in neutral but not in park as well. And interesting that it happens with stock head unit which (in theory) weeds out an issue with the aftermarket wiring. It seems like there is a ground issue that affects the parking light circuit when the brakes are depressed, that then affects the head unit illumination circuit. I think the head unit illumination circuit is the same as the dash lights, do any of your buttons on the dash or hvac or gauge flicker with brake light? I could be wrong on that though. Maybe it's a CANBUS issue... i have no idea how that stuff works but maybe it can get someone else thinking.

 

My thought is that stop light power is feeding back to the park / tail light circuit at less than 12V due to a loss of a good ground on one of the tail light assemblies, or a bridge of corrosion in a connector, such as the trailer socket. Either would certainly cause these symptoms, that’s why I suggested the things I did.

One more thing @drpheta could try, is to temporarily unplug the connector to both tail light assemblies and see if the dimming issue goes away. If it does, plug them back in, one at a time, to see when it comes back.

 

I'm going to try that this week when I get a chance. That's a great idea