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Dave Nova
Dave Nova, ASE Certified Tech
Category: Toyota
Satisfied Customers: 19450
Experience:  ASE Master Certified. 25 yrs experience
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my brake lights wont work when my headlights are turned on.

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my brake lights wont work when my headlights are turned on. they do work with the headlights turned off. all other lights work fine. also, my third brake light works fine either way. how can i fix this?
This is due to a bad ground for the taillight circuit. With the taillights off, the brake lights will pull a ground through the taillight circuit. With the taillights on, there is no ground available. Check for a good ground at the white/black wire for each taillamp connector. If there is a good ground at the white/black wire, the problem is in the bulb sockets. If there is no ground on the white/black wire, the ground will need to be repaired.
Customer: replied 6 years ago.
im not sure if this could change anything, but i have aftermarket taillights which have led brake light rings, and seperate wires for the running tail lights. so, in order to make a connection where the led lights fire as brake lights i connected them to the original taillight circuit wiring and then made a seperate circuit all together for the running tail lights. so the taillights and the brake lights are two seperate circuits. does that make sense? everything worked for a long time, im not sure when it stopped working or why. basicallly the taillights are running constantly. when i press the brakes the led rings light up. but now when the headlights are on at night the led ring brake lights dont light up. im just giving more details to see if you have any other ideas. otherwise your answers good.
Since they work with the taillights off, your problem is a bad ground. Check connections at the white/black wire at the taillights. Try taking a jumper wire connected to ground on one end, then connect to ground wire at brake light. If the brake lights then work correctly, you have a bad ground.
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