LED Third brake cargo lights will not turn off?

MSTONE1700

MEMBER
2018 FORD F-250
6.7L
V8
4WD
AUTOMATIC
155,000 MILES

I just replaced my factory 3rd brake light with an LED 3rd brake light. Everything works great, but the cargo lights won’t turn off unless I shut off the truck. They won’t turn off when I put it into gear and drive. And just always stay on now. In addition, the cargo light switch doesn’t work when the LED 3rd light is plugged in.

My question is there a way to stop get the cargo lights to function normally again? Can I add a resistor or something to it or change something with the wiring to fix this? I really like the light and want to make it work. But I could also try to buy another brand and see if it is the light itself.

I’m totally open to advice and suggestions please.

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,205 POSTS

Hi,

When you change from an incandescent bulb to LED, the voltage requirements are very different. The LED requires a small amount of power to work.

Just out of curiosity, if you reinstall the original bulb, does everything work normally? If it does, then I suspect you need to install a resistor before the LED light to absorb the unneeded power.

I'm not sure of the original bulb wattage requirements, but I suspect you will need somewhere around a 5-watt resister for this. Keep in mind, when in use, it is normal for the resistor to get warm, so place it on something that won't be affected.

Let me know if that helps.

Take care,

Joe

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Thursday, September 7th, 2023 AT 7:10 PM

MSTONE1700

MEMBER
3 POSTS

Thank you for that info. And yes, when I put the factory light back on it all worked normally again.

I’m also not sure if the wattage is needed but where can I find a resistor that will work for this light?

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Thursday, September 7th, 2023 AT 7:13 PM

JACOBANDNICKOLAS

MECHANIC
108,205 POSTS

That is where we need to know the original bulb wattage and what the LED requires. The original bulb may have it written on it. Once that is determined, then we need to lower the wattage of the LED to mirror the original bulb's requirements. If I had to guess, I would think a 5w resistor would take care of it. Please understand, that is in theory.

So, if the original bulb was a 5-watt bulb and the LED requires 1-watt, we need a resistor that will eat up the 4 watts not needed.

Let me know what I can do to help. Also, if you have the bulb number, let me know what it is. I'll try to determine the wattage.

Take care,

Joe

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Thursday, September 7th, 2023 AT 7:24 PM

MSTONE1700