This is a pretty strange one, but hoping one of y'all has experienced something similar.
Seemingly at random, I will be trucking down the road and when I hit the brake pedal I lose electrical power VERY briefly. Radio restarts, speedo blips to zero and back immediately, and in rare cases I can even feel a slight miss in the engine. I know it is electrical, not vacuum related, because it has also happened when I hit the turn signal. So that little extra power draw to those circuits is causing the problem. Interestingly enough, I can't find any other characteristics that will cause this to happen consistently. Running with headlights on, A/C full blast, interior lights on, wet/dry/hot/cold weather, etc. - doesn't seem to make a difference. Happens when it wants to happen. Sometimes I will go a couple of months with it never happening, other times it happens 5 times on my morning commute. Been going on for a couple of years, because I can never duplicate it for someone to check out, but figured I would seek the wisdom of the innerwebs.
I have not done a lot of troubleshooting, but I did replace the battery about a year ago (routine) and replaced the clamps at that time and it didn't seem to behave any differently.
Any thoughts on where I should start?
My thoughts are cables, grounds, alternator, ?? - but I don't want to just start replacing stuff with no real plan of attack.

 

Does your truck have a Volt meter??

If so do you see a voltage dip ??

In any case it never hurts to upgrade all the positive cables the B terminal of the Alternator to the fuse block

The ground cables as well

I use Marine Terminals on all my Vehicles

It seems like your losing the main ground or output of the alternator. intermittently both will cause the same problem

No brake and charge light being on when this happens

 

What would the alternator have to do with the brake pedal?

Cables? Grounds? Well, that narrows it down to 100% of the electrical system, so I guess you're making progress.

If the only trigger is the brake pedal, then I would be almost certain you have a short somewhere in the brake light circuit. The brake switch does connect to the ECM, but that's pretty protected. Unlike the line back to the brake lights, and the lights themselves.

I would start with carefully removing the brake lights, and examining the sockets and wiring. Then try to visually inspect the wiring all the way from the brake lights back to the cabin.

UNLESS you have a trailer light connection. In which case I'd bet money that is the location of your problem.

 

It does have a volt meter, but I can't say I've ever seen it move when this happens, but I'll be on the lookout next time. It is just so small in comparison and happens so fast.
I'll start with cables and connectors since that is relatively inexpensive...I hope.

 

Thanks for the reply. I guess I wasn't clear enough. The brake lights are not the only thing that triggers it. As stated in the OP, the blinkers will do it sometimes as well. But are you saying that a problem in the brake wiring could cause the entire electrical system to blip out and come back like this, including the ignition sometimes? I can check all that for sure, just trying to understand.

And no, I don't think the alternator would be causing this if you mean the brushes/stator kind of stuff, but maybe a bad/loose connection or something.

 

If you have an intermittent short in the brake or turn signal (or any other system), it can cause a voltage drop sufficient to drop the radio, but it will be so quick that it might not blow the fuse. (It's a 15amp fuse, assuming it has the right one, so it will take a few milliseconds for the alternator/battery to boost up enough power to actually blow the fuse.) I'm assuming that the short is when a wire "bounces" against a ground, which will be pretty short.

Are there any other triggers than brakes and turn signals? Both of those point to the tail-light fixtures. While you don't live in the snow and salt belt, something as simple as a small crack in the lens can let in enough water over time to cause a problem.

I could be all wrong and inviting a wild-goose chase. But problems with the alternator output shouldn't do anything; the battery will hold up the voltage so that the radio/speedo/etc. will never notice.

 

No, that's a good point and I appreciate the explanation. I don't think anything but brake and blinker triggers it, so that sounds like an easy place to start picking through. I may not be in the snow and salt belt, but I do live in the mud belt

 

I had same problem with using turn signal, radio would go out, then come back on. I switched out alternator, and problem went away. The volt meter is definitely higher with replaced alt. FWIW my alt had 245K, I replaced with Denso alt with 191K on it ($23 shipped). From what I've read the after market ones aren't worth it. Your Denso can be refurbished, possibly new brushes or whatever...

 

So I did a little more digging and then the truck gave me another data point I checked for loose connections or corrosion in the tail light circuits and all wiring and connections looked really solid. I know there is much more to it than just looking at it, but before I could dig in any further I was driving home from work the next day and when I turned on the fan to give me some heat, everything went dark for a split second, even the ignition missed a few firings before everything came right back. At this point I also noticed that my headlights were kind of "pulsing." Not a predictable pattern, but just dimming and coming back a few times per second. It is not easy to notice when city driving, so it might do it all the time, but that was the first time I noticed it when out on a country road.
So if turning on the fan would do the same thing, I'm not sure the tail light circuit is worth pursuing any further. It seems to just be when the system gets a surge of power to some device like blinkers, brake lights, fan, etc. And with the headlights pulsing, could that be something with the voltage regulator? Isn't that in the alternator?

 

Lots of threads about intermittent electrical issues being traced back to worn alternator brushes. One example at http://www.4x4wire.com/toyota/mainte...nator_brushes/ but lots of others out there too.

Brushes are pretty cheap and easy to install...getting the alt out and back in is the hardest part. Part 27370-35060 is a holder with the brushes installed and is about $15.

http://parts.toyotaofdallas.com/oem-...MDMwNCZyPTY%3D

 

Just circling back to this really old post because I never gave my solution. I replaced the alternator with an aftermarket just for kicks and it has been fine for 4 years. All of the strange behavior went away. Hope that helps someone else if they find themselves chasing gremlins.