2012 Prius 4 purchased 2017, Not sure if OEM 12v When I press brake brake lights come on, but not sure if it is the switch. Could this be battery related? Or something worse?
I don’t see ready illuminated, is your foot on the brake pedal? Does the dome light come on? Any recent maintenance or damage?
Dome lights do not come on automatically, no recent maintenance or damage. The ready light is that green glow at 56 seconds. The little spotlight does come on, but flickers like the dash lights when I press the brake pedal
I’d definitely start by replacing the 12V battery. It’s due for replacement at that age and it can definitely cause what you’re seeing. It’s a special battery, installed in the rear right side of the car (hatch area). You could try charging it, but I’d just buy a new one and most likely you’ll be on your way.
Check the voltage on the 12 volt first, with a digital multimeter. At the under-the-hood jump point in fuse box. Do this first thing in the morning, pop the hood the night before: that way you'll access the engine bay without "waking up" the car in any way. Rolls Royce would be to hook up something like a Solar BA5, directly to the battery posts. Besides reading the voltage, this will do an electronic load test of the Cold Cranking Amps, and give you a verdict.
