Does anyone know what would cause my third brake light to not light up? It only appears to light up when I have my headlights on, but when I'm driving around during the day with no lights on, the 3rd brake light will not light up. Some kind of shortage going on here?

 

Did you check the bulbs?

 

+1 for checking the bulbs. After replacing those, check the fuses if its still giving you problems.

 

LOL at initial advice!

So are you guys suggesting that his bulbs may be burnt out ONLY during the day?

To original poster...... How do you know it only works at night? Are you sure you just can't see it during the day? Did you have someone in the bed looking at it when you're hitting the brakes? If it's bulbs or the fuse, it will not work at all. If it's a wiring issue, it could only work while your lights are on.

 

Here's your sign!

 

What does "It only appears to light up when I have my headlights on," mean ? Does it light up or just appear that way? geez.

 

No, what I mean is that the bulbs in that third light that come on with his running lamps (headlights) are ok, but that the bulbs for the brake lights are burned out. So at night, when he has his headlights on, he sees the working bulbs, but during the day when those bulbs are not on and he hist the brakes, he doesn't see anything because those bulbs are burnt out.

 

I think you guys are confused.
If we are talking about the 3rd brake light (in the center of your cab, above the rear window), there are no "tail light bulbs" which would be on when his headlights are on. There's only a brake light which should ONLY LIGHT UP when you hit the brakes, and the cargo dome light which comes on when you turn it on with your dimmer switch.

 

Ok so this is whats up with my ride Somehow the seal srunk or somehting but ther was a gap at the top of the light and water was getting in causing the light to short circuit and rotting out the rockerpanells so i had to make a new gasket that was bigger to seal it try cheaking if u have the same prob Hope this helps

 

I have had my brother check this on more than one occasion. It's quite honestly just screwed up. Sometimes the third brake light will light up with the headlights off too, it's almost like it's just hit or miss.