3rd brake light always on

obs7.3 · Jun 20, 2012

I put in a LED third brake light and cargo light and had to splice it into the stock wiring in the roof. but whenever my truck is running the 3rd brake light is always on. it gets brighter when I step on the brakes. it's like i tapped it into the parking lights or something (but this is the only light that's on whenever the truck is running) but I checked the wires and there's just the 3 power wires and 3 grounds.
i'm not sure if the stock third brake light did the same thing or not cuz the bulb was blown in it when i swapped it out but i never noticed it before the bulb blew. i've been told to add a resistor, would that solve the problem? and what size would i need?

Arisley · Jun 21, 2012

Moved this to where you might get some better help.

7.3psd97444 · Jun 23, 2012

Get a test light and poke the wires. Figure out your ground and be done with that. Find the one that is certain to be the dome light. Opening and closing the door with the test light probe poked in the wire the test light should go on and off with the dome light. Then find your brake lights. Same way poke around till you find the one that only lights up when you push the brake.

obs7.3 · Jun 27, 2012

i don't think i'm understanding what you're telling me. if i know where the ground is, and which 2 wires are the dome light. and which one is the brake light. how do i get the brake light to only work with the brake pedal? i know it's wired correctly now cuz when i watch the light and someone steps on the brake pedal (with the truck running) the light gets brighter. and the cargo lights never come on unless a door is open or i turn the cab light on with the headlight dimmer switch.

7.3psd97444 · Jun 27, 2012

Gotta be the wrong wire then. It should not get continuous power. It should only get power to come on when the brake pedal and brake lights come on. I was suggesting using a test light and poke the different wires untill you find the one that DOES NOT have continuos power, but does get power when the brakes are applied. That will be your winner.

obs7.3 · Jul 1, 2012

OH! okay i understand what you're saying.
sorry about that. :doh:

7.3psd97444 · Jul 1, 2012

obs7.3 said:
OH! okay i understand what you're saying.
sorry about that. :doh:

ITs ok man Im just trying to help. :ford:

obs7.3 · Jul 3, 2012

haha it's much appreciated.
is the 3rd brake light wiring spliced into the dome light inside the cab?
i'm wondering if i'm getting feedback somewhere if they are.

Viking · Jul 3, 2012

It's odd that its just the 3rd brake light

7.3psd97444 · Jul 3, 2012

obs7.3 said:
haha it's much appreciated.
is the 3rd brake light wiring spliced into the dome light inside the cab?
i'm wondering if i'm getting feedback somewhere if they are.

yes its one harness going up the side of the cab and to the back. If you look driver side bottom cab corner you can find the harness back there. It goes along up the side to the dome and then out to the 3rd. Think theres 5 or 6 wires total