Headlights Dim and RPM's Drop when Applying Brakes

I have a 2020 TRD Off Road with 47K miles. My dealership replaced the battery 6 weeks ago (with a Toyota battery) since the other one was going bad. Since that time, I've noticed that when I am driving at night and apply the brakes, my headlights quickly dim and my RPM's drop every so slightly. I looked at the connections on the battery and everything looks fine. I have an appointment to take it in to have it looked at, but if there is a simple fix someone may be aware of, I can save myself a few hours Saturday morning and instead of sitting at a dealership, I can enjoy my Saturday.

 

Sounds like a charging system problem; or perhaps a draw on battery that is killing battery. I would say battery is losing power by either not being charged properly or an electrical draw killing battery.

 

Yeah, I was thinking that may be the case. I've had that before with another car where a door sensor had gone bad and it was causing the vehicle anti theft system to go haywire. And it drained the battery. I wouldn't think on such a young Toyota 4Runner that I would have that issue quite yet though.

 

I second this, check voltage regulator and charging current.

 

My first thought is the alternator.

 

Thanks y'all. I appreciate it. Luckily I purchased an extended warranty so if it is the alternator or something else, I should be covered.

 

Any aftermarket accessories connected to the electrical system?

 

4Runners are very temperamental when it comes to power, especially through the battery terminals. Remove terminal connections. Visually inspect, clean, mechanically scour and reinstall tightly.

Many a member had had electrical issues here and looked at the terminals and said "looks good" and went down a huge rabbit hole chasing gremlins, only to find out there was a thin layer of corrosion causing all the problems.

Start simple and go from there.

 

Great advice. Thanks. And to answer the other question, nope, straight stock. No aftermarket installs on it.