Truck wont start, brake shuts off power

Went to start my 2015 tundra today and got nothing. Thought maybe left lights on and battery dead. Neighbor tried to jump start it and sound like battery was dead and wouldnt crank more than a couple time. Noticed when I turned the key I had electrical power but the moment i touched the brake everything turned off. Still no start. Ive tried everything. Put the charger on the battery and says its 100% charged. Would think its the battery except for the brake pedal shutting down everything.

 

Might be just that dead that the brake lights are killing what little charge you have in it.
If you have a volt meter see what the charge is at the battery. If you are showing good there you can start searching for a short.

 

I can turn off the key and reproduce it. I turn the key and will here once click and it goes blank as well. Im thinking bad battery but the brake thing has me stumped. If I turn the key and dont touch anything the dash lights up, radio will come on and heater works. Minute I touch the brake pedal everything shuts off , even the dash lights.

 

Check for a blown fuse, could be 1 of the 2 for a tail light. Should be labeled "brake or park".

 

Dont see any blown fuses. It will shut down if I try to take it out of park or try to start it as well. Wont even crank. It did crank a couple times when I had it hooked up to jump start. I can hear the relays hum after I try to start it.

 

It's the battery. You have a dead cell. Takes all six cells to crank. Is it the original battery?

 

Im thinking it is. Says toyota on it. I bought the truck with 50000 miles on it and now have 83000. Would a dead cell caus the dash to work them not to when trying to start it?

 

There you go. Not surprised. You got one of the last good batteries Toyota put in a Tundra. Lasted five or six years. Now, if it was a 2019, I wouldn't be surprised either. Crap 24 month batteries since about 2016.

My personal experience is a weak/nearly dead cell battery can power the dash for a short time, then clicks from the starter solenoid, then nothing. Takes a certain minimum power to run the ignition system. You step on the brake pedal and the stop lights steal enough to stop the ignition system. Makes sense.

 

So just went and turned the key and looked at the voltage on the dash. Needle barely moved. Maybe to 10 volts. I think you hit it on the nose with a bad cell.

 

See my edited post above.

 

100% battery...evades logic? Yup, it's the battery man...

 

Ding Ding Ding ! Bad cell in the battery. $185 later it starts right up. Thanks for all the input guys.

 

fantastic thread.

I'm amazed at the goofy things not only Tundra but other cars will do with even a slightly out of spec battery.