3rd brake light problems

[Big Jon 95]

I got a 3rd brake light for Christmas and when I went to plug it in the red leds turned on like I was pressing the brakes. When I open the door it turns off and will turn back on when I close the door. Any thoughts as how to fix it or what is causing the problem?


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[Thatfordguy]

I had the same issue from an led I got off of eBay. I unhooked the yellow wire on the light and everything works as normal.

 

[Big Jon 95]

That fixed it, thanks!


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[W8TVI]

I did a little research, and I have found out why this style of LED 3rd brake light works this way.

They have the circuit and the light setup to make it have "running lights".

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From this wiring diagram, they are hooking up the brake lights to D and B like it should, but they are hooking up the cargo light from C to B.
Normally this would be fine, but they are hooking up another circuit that causes the brake light to burn a lower level than full on from A to B.

I checked the voltage available from A to B, and when the dome light is turned off, there is 10 volts present between A and B.

 

[Thatfordguy]

So another thing that I can't remember from my previous 98 and both factory bulbs were burnt out in my current truck but are the cargo lights supposed to come on when you open the door?

 

[W8TVI]

So another thing that I can't remember from my previous 98 and both factory bulbs were burnt out in my current truck but are the cargo lights supposed to come on when you open the door?

Not on this '98 Sierra. It only comes on with the cargo light switch on the dash.

 

[Big Jon 95]

I had another brake light like the one I just put in and it worked just fine and I didn't have to remove a wire. The cargo light would only work when I had the switch flipped and the door open. After I pulled the wire out of my new one the cargo lights turn on whenever I flip the switch


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[mars2878]

any pics of the light?

what brand is the unit?

 

[Actjack]

I had the same exact issue when i replaced my third light. I took my new light apart, and moved some of the wire connectors around. Now it only comes on when i press the break pedal or when i activate the cargo light...and im fine with that.

 

[Thatfordguy]

any pics of the light?

what brand is the unit?

Mine is a smoked one that I got off of ebay