Truck Brake Lights working, Trailer NOT

[lakelaurashawn]

Good Afternoon.

I have been reading this forum for the last two hours to see if anyone had a similar problem and I could not locate one. Seems that there is a lot of good experience here and maybe you can help.

I have a 2001 Chevy Silverado with the 8.1L engine and Allison transmission. It is a crew cab and a long bed - I am the original owner and the truck has about 45,000 miles on it; It is not a daily driver. In reading around I see that a lot of the responders like to have an understanding about the truck and its use - I hope that works.

So here is the issue. I have a trailer that I tow and the other day at a stop light the driver next to me said that I did not have any brake lights. I pulled over and being the only person in the truck, I checked the blinkers - first the right then the left and they worked fine on both the truck and the trailer. I thought the guy was messing with me because I could see the reflection of the truck brake light from the truck on the trailer when I hit the brakes. Went on home and got my wife to get in the car and check the lights again - both blinkers work, however the trailer brake lights do not work (the truck brake lights do work). The trailer lights do not have a separate amber and red light for turn and brake so if one is working shouldn't the other...?

Here is what I have done to solve the problem. I replaced the seven pin cable on the trailer. I have removed the Prodigy connections and cleaned them. I have removed the trailer plug wire connection and cleaned it. I checked each brake light for dirt and grime, cleaning where necessary. I checked the fuses under the hood (there was not a trailer brake fuse, just a LT and RT fuse) those too looked fine.

I then asked my neighbor if I could borrow his truck and hook it to my trailer. We hooked up his truck to my trailer and everything worked fine. This leads me to believe that the issue is with the truck and not the trailer.

Any suggestions on why the truck brake light is working fine and the trailer brake light is not working?

Thanks in advance.
Lake

[mudseeker]

well you should only have to concern yourself with 4 of the wires.

they are green, brown, white and yellow.
white is your ground and since you have turn signals i wouldn't worry about that wire.
brown and yellow are your turn signal and as you mentioned work, so i would not worry about those either.
the one i believe is causing your problems is the green wire, which is your tail and stop lights if i remember right.
do you have tail lights when you turn your parking lights on?

i would start back probing your trailer wires at the connector with a test light and see if the green wire is getting power to it.

[lakelaurashawn]

Thanks Mud Seeker.

Yes, I do you have tail lights when I turn the parking lights on.

I will trace the green wire to see if it gets power when I depress the brake pedal.

[CharlyG]

My jack(truck) was so corroded I had to replace it. I tried cleaning, just too much work, and it never lasted. It was never the same pin either, just any particular trailer light that didn't feel "connected"! Ha!

[lakelaurashawn]

Does the hazard circuit have anything to do with the brake light?

[CharlyG]

In the sense that they both turn on the same lights, yes, but otherwise, not really. Brake lights, turn signals, and emergency flashers all use the same bulbs/brightness. The tail lights, only use half the bulb, or one of the two depending on model.

[leolkfrm]

does the truck have a 3rd brake light? if so you will need the adapter for splitting the lights

[stelmadl]

did you check the ground? i know alot of trailer wire adapters omit the ground wire (or you see it dangling) because they are depending on the ground from the truck....connected through the hitch. if your hitch is rusting, or is loose in the receiver, etc. the lights will do funny things if the connection is not "sound." just a thought.

[lakelaurashawn]

Yes, my truck has a third brake light - it in functioning correctly.

Thanks for the idea on the ground, it appears to be solid. I took it off the frame, used a small grinder to remove any debris. I then cut off the eye flag and replaced that with a new one - still non-op trailer brake lights.

My hazard switch does not appear to be functioning correctly.

[Moostang]

Did you check to see if you are getting the power to the truck side of the plug from the truck itself. I would check all and even make sure you are getting a good ground on that side. If you are getting power (just using a light tester) then make sure it is the right amount of voltage. Make sure you test all of this with someone pushing on the brake.
If you are not getting if at the plug, then I would test the wires right behind the plug to see if it is the plug or not. If not, then work your way back.
If you are getting the proper power then I would test the power on the wires on the other size of the trailer plug, it may be that your tester is getting the power in the plug, but the connectors may be bad so the normal plugs are not getting a good connection.