HVAC controls light up when I brake

This is a strange one.
When I hit the brakes, the backlighting for the hvac controls lights up.
Also, when backing up, when i hit the brakes, the camera display dims and the radio gets quiet.

maybe the semi-muting is built into the head unit for safety when backing up, but certainly not the display dimming. Just trying to lay out all symptoms.

Has anyone out there seen this before?
2004 Taco.

Thanks

 

Does the backlighting for the HVAC controls turn on normally with the DRLs/headlights? If not, I'd suspect those lights somehow got tied into the brake light circuit instead of the running light circuit. No clue how that would happen, but that's the first thing that comes to mind.

Not sure about the backing up part, but all of those losing power at the same time sounds to me like some other load is coming onto the same power source & reducing current.

 

It does happen with lights on or not.
Hitting the brakes os somehow draining the radio display.
Tomorrow I will document all symptoms. I did, but firgot since this morning!
I better write things down and update.
In reverse, the backup cam dims only when i hit the brakes, rendering the display useless.
I will probably have to staet pulling fuses, but will definitely post all symptoms tomorrow.
Thanks.

 

I had this on my 96. Check and clean grounds on both taillights. The brake and marker light share a ground at the housing, when that ground gets isolated from chassis/battery -, hitting the brakes bleeds some voltage over to your accessory/marker light via the bulbs.

mid you unplug the twilight housing and it stops, you’ve identified the culprit there.

if the ground at the housing is ok, I believe the harness grounds back at the driver side kick panel and you should check those connections to the body there. hoping somebody with the electrics book can provide better detail on that.

 

Thanks Mike.
Grounds make sense.
I didn't understand when you said "mid you unplug the twilight housing and it stops, you’ve identified the culprit there.".

Here is the situation:

Wìth the lights on, nothing acts up.
When the lights are off, when I hit the brakes the guages, the heater controls backlights, and the shift indicator lights all go on when I hit the brake pedal and the radio dims and mutes some.

I like the ground tracing direction though.

Doesn't Toyota have some program where for around $25 for 2-day use of the manuals or am I just crazy?

Thanks alot.

 

Jeez sorry, early morning auto correct chaos-

IF you unplug the entire housing from the harness, and problem goes away, look at the wiring on the housing (many shared grounds amongst the different lights). If it persists, look at chassis grounds at driver footwell(I think…I don’t believe there are any wires connected to sheet metal behind the driver/passenger footwell ground points, but could be wrong!)


Your symptoms are precisely what I had on my 96!

I have the wiring guide on my computer somewhere but it’s 100 miles away right now. There is a link to it out there somewhere…

 

Also- take the brake light bulbs out (dual filament), and see if problem persists. With the dual filament ground point floating/loose, the brake light power back feeds into your accessories lights via the other filament in that bulb (tail light marker)

 

Wow, cool idea.

I will start with the tail lights because it is a quick test (path of least resistance pun intended).

Grounds, very encouraging ideas.
I really appreciate this.

 

This pdf service manual is 640 pages long and stresses full electrical info.
Anyone try this?
$37.00 is definitely better than forking over $300 plus for the real set.

https://www.ebay.com/itm/375955499276?_skw=2004+tacoma+favtort+service+manual&itmmeta=01JNNSQCDKTMZFCCH4GAMB06Y4&itmprp=enc%3AAQAKAAAA4FkggFvd1GGDu0w3yXCmi1eqWPZs4MCKKqUJmUBs%2FBV4bxB3TGKtr3E1GQquPYO+adqUGR0IaTpvuxvkXoDPOkX7icazBegRvkwTmNOEFW%2F225c1VfWQfQHmGOglofBsRONmQVFssQA%2Fh9bYYnRsGKTWS1wMcg9n1nSm2PrApdUluccY2oNL+26VWEMBCPeY2m4O%2F82fwRu38je4C0E9kkhG1ejIP77X04faXeR8FQxk9iAeeo6eGoc72AcdrBDtk+L7GtYvzaFjdwSzMEZg5BR2opw%2F2qhR7aUCFVO7XMgX%7Ctkp%3ABk9SR9zI3bmtZQ

 

I will go through the steps above.
I might have some more questions on the testing.

Worst case scenario is that I leave the lights on!

Thanks

 

If it has the electrical diagrams it’s worth getting for your truck, makes troubleshooting and mods super easy!

 

If it has a trailer brake light converter behind one of the taillights, remove it and see if the problem stops. I had one on a 1st gen that got water in it and every time I stepped on the brake all the dash lights came on.

 

Great call.

 

Hmm, you might be onto something. No converter harness, but I did wire in a backup cam. Thanks

 

It claims to have wiring diagrams, but so does the pos Haynes one.
Who knows what that ebay offering has.
I might look on ebay for just the factiry wiring=electrical manual.

 

I found a 2004 electrical factory manual for $65.00.

Let's just hope it is what it says it is.
Maybe I can help others with it.

I will update