Wiring third brake light...help! - Fiberglass RV


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Old 01-11-2020, 10:34 AM   #1
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Name: Dan
Trailer: Scamp
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Wiring third brake light...help!

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I bought a cheap chinese made third brake light for my scamp. It is 3 wires; "ground", "light on" and "light pulsating". I sealed off the light pulsating wire. I tried to wire the "light on"to both my green wire and yellow wire to brake lights to ensure it was attached to both sides of the brake circuit. I had previously rewired scamp with led light kit and full 4 prong harness from walmart. That all works fine and so does third light when i test on a remote battery.
Here is the problem- I can't get third brake light to come on with brakes. I guess i don't have it wired right.
How do I wire this thing to work? I am fine if it blinks when the turn signal is on. I just want a third brake light for safety.
Thanks in advance for your advice.
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Old 01-11-2020, 10:59 AM   #2
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Name: bob
Trailer: 1984 u-haul ct13; 1996 Casita 17 Spirit Deluxe; 1946 Modernistic teardrop
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Try wiring it to only either the green or yellow, not both. Better yet, throw it away and get a light bar that is everything and mount it above the rear window. I installed one on both our Uhaul camper and Casita. It is LED and is 3 markers, left and right turn signal, and stop light.
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Old 01-11-2020, 11:25 AM   #3
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Thanks. I like it inside the spare. I assume I just wire the ground to the frame and try the yellow?
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Old 01-11-2020, 11:49 AM   #4
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Just to simplify and even add safety, why not simply add two lights at the top and either end of your rear window.
You can buy led short strip taillights for cheap.
You would then have full function tail lights, brake lights and turn signal lights. They are brighter than stock and can be bought in various sizes.
Here's what I chose...
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Old 01-11-2020, 12:12 PM   #5
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Name: Terry
Trailer: 1971 Hunter compact Jr, 1979 Terry 19', 2003 Scamp 16'
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Check to be sure you have a good ground at the frame by going from the positive on the battery to the frame with a volt meter. While brakes are active go from each of your wires to the frame to check which has good voltage. You'll have your supply. It's possible that the other wire is running lights. Turn on your running lights and go from that wire to ground to check for good voltage again.
This is a simple way to check.
I would not want to make holes, either.
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Old 01-11-2020, 12:28 PM   #6
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Quote:
Originally Posted by Terry in Fowler View Post
Check to be sure you have a good ground at the frame by going from the positive on the battery to the frame with a volt meter. While brakes are active go from each of your wires to the frame to check which has good voltage. You'll have your supply. It's possible that the other wire is running lights. Turn on your running lights and go from that wire to ground to check for good voltage again.
This is a simple way to check.
I would not want to make holes, either.
The OP has wired the trailer with 4-plug wire, the ground should go to the white wire in the harness.
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Old 01-11-2020, 01:04 PM   #7
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Third brake light

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Originally Posted by Dan in Philly View Post
Attachment 132780






Here is the problem- I can't get third brake light to come on with brakes. I guess i don't have it wired right.
How do I wire this thing to work? I am fine if it blinks when the turn signal is on. I just want a third brake light for safety.
Thanks in advance for your advice.
We would need to know the light model to answer, From the description it sounds like you need to add a converter to drive the light from both left and right lights.


https://www.etrailer.com/question-113298.html
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Old 01-11-2020, 01:04 PM   #8
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There are Third Brake Lights, and Third Brake Lights!

I had some similar issues. Pretty sure that my problems were somewhat similar to yours.

I also bought a third brake light, as I wanted my Trillium to be a bit more obvious on the road. A little different from yours, mine only had 2 wires, as there was no European/overseas flashing mode. These are generally made it be installed directly in a vehicle where the brake lights are separate from the turn light circuit.

The big problem is that the light is only PART of the solution, particularly on our trailers, where the tail lights offer turn OR brake mode in the same bulb filament. There is usually a second filament in the bulb for running light. The third light is only supposed to come on when the BRAKES go on, but if you hook it to one side or the other, it will light when either the brake or the signal goes on. You need a secondary device that will connect to BOTH left and right tail lights, and this unit will sense whether only one light (signal light) is activated or both (brake mode). Of only one light is activated, the third light is left unpowered. If both left and right trailer lights are activated, power is sent to the third light.

Stop Logic makes several, like this:

Brake Lamp Stop Logic Module [AT-LC-1] - Starcraft Parts

I just went to a local truck cap store, told them what I was doing, and they sold me what I needed. It was easy to wire (it fit inside, under the dinette seat), and I was able to run the wires inside up to my third light very easily.
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Old 01-11-2020, 02:04 PM   #9
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Got it fixed. Attached to yellow and got a good ground and it works! Thanks!
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Old 01-11-2020, 02:33 PM   #10
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Third brake light

Curt gives a good description IMO. It does sound like you are having a ground problem but I am not an expert on trailer wiring. This seems like a good item to isolate the brake light only.


https://www.etrailer.com/Accessories.../PP20-702.html
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Old 01-11-2020, 04:09 PM   #11
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Like Floyd said, the ground should be connected at some point to the white wire in the harness, which will ground the light back to the tow vehicle ground. Ground wires attached to the trailer frame can eventually corrode. Another point that Floyd may agree with; my reason for a high mount stop / turn light is if a big truck is following close in traffic the driver can't see low mounted trailer lights over his truck's hood. I've experienced this myself, and had a couple truck drivers agree. One driver even admitted to bumping a trailer a few times at a toll booth because he couldn't see it over the hood of the long nose Kenworth that he was driving.
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Old 01-11-2020, 06:26 PM   #12
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Quote:
Originally Posted by mary and bob View Post
Like Floyd said, the ground should be connected at some point to the white wire in the harness, which will ground the light back to the tow vehicle ground. Ground wires attached to the trailer frame can eventually corrode. Another point that Floyd may agree with; my reason for a high mount stop / turn light is if a big truck is following close in traffic the driver can't see low mounted trailer lights over his truck's hood. I've experienced this myself, and had a couple truck drivers agree. One driver even admitted to bumping a trailer a few times at a toll booth because he couldn't see it over the hood of the long nose Kenworth that he was driving.

LIKE!
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Old 01-11-2020, 06:52 PM   #13
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Originally Posted by mary and bob View Post
...One driver even admitted to bumping a trailer a few times at a toll booth because he couldn't see it over the hood of the long nose Kenworth that he was driving.
I hope someone (preferably with a badge) explained to him that he was following too close.

NY Veh & Traf L 1129 (2012)

1129. Following too closely. (a) The driver of a motor vehicle shall
not follow another vehicle more closely than is reasonable and prudent,
having due regard for the speed of such vehicles and the traffic upon
and the condition of the highway.
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Old 01-12-2020, 07:02 AM   #14
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[QUOTE=gordon2;765042]I hope someone (preferably with a badge) explained to him that he was following too close.

NY Veh & Traf L 1129 (2012)

Nowhere did I say this incident was in NY, which it was not. It was at a multi lane toll booth prior to the invention of EZ Pass so involved stop & go traffic making cash payments. The trucker actually had left space, but as is typical, leave a space and someone will go into it. In this case the driver pulling the little flatbed trailer pulled in front of the truck from the right and the truck driver could not see the trailer. After getting bumped a couple times the driver of the car got out and hollered at the trucker who got out to see what the problem was and apologized to the car driver. Also typical that if there is an incident involving a big truck, the trucker is automatically deemed to be at fault. And no, I was not the truck driver in this incident, I was the shop manager on a lease account so I got to hear all kinds of stories from my drivers.
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Old 01-12-2020, 07:51 AM   #15
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[QUOTE=mary and bob;765076]
Quote:
Originally Posted by gordon2 View Post
I hope someone (preferably with a badge) explained to him that he was following too close.

NY Veh & Traf L 1129 (2012)

Nowhere did I say this incident was in NY, which it was not....
No worries.. the same law exists about everywhere. In fact I started to post the statute from my home state but then looked up the NY statute and guess what... it was almost exactly the same, word for word.

Anyway the truck driver was clearly at fault and in violation. And no, truck drivers are not always considered at fault, but this one was. Its too bad that someone jumped into the space in front of the truck, but the truck driver was required to sit still until he could see the roadway and know it was safe to proceed. The only way the truck driver would not have been in violation was if both vehicles were in motion and the first one cut in front of the truck and then slowed or stopped so abruptly that the truck could not get stopped in time to prevent contact.

And it was pretty clear you were not the truck driver. That was not even suggested.

Quote:
Originally Posted by mary and bob View Post
..... After getting bumped a couple times the driver of the car got out and hollered at the trucker ...
I have to wonder how many bumps are required before the truck driver figures out there is a vehicle in his blind spot. Frankly, its beginning to sound a little like pay back for cutting in line. Dangerous action regardless for a number of reasons.
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Old 01-12-2020, 10:20 AM   #16
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Quote:
Originally Posted by gordon2 View Post
I hope someone (preferably with a badge) explained to him that he was following too close.

NY Veh & Traf L 1129 (2012)

1129. Following too closely. (a) The driver of a motor vehicle shall
not follow another vehicle more closely than is reasonable and prudent,
having due regard for the speed of such vehicles and the traffic upon
and the condition of the highway.
You really don't have to be too close in a large truck, even a fullsized 4WD pickup, to not be able to see the lights on many fiberglass trailers when in heavy traffic. That's why I have full function lights up by the rear window on my Scamp. I would rather have the upper lights than the lower ones if I had to choose.


You are right though, tailgating is a real problem, especially when the taillights ahead can't be seen.
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Old 01-13-2020, 06:36 AM   #17
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My setup
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Old 01-13-2020, 06:52 AM   #18
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Looks good Kevin. Where & how did you tap into the original wiring?
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