How to reverse polarity in running/ tail lights? - Fiberglass RV
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Old 05-11-2018, 03:33 PM   #1
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Name: Nigel
Trailer: Scamp 13
Minnesota
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How to reverse polarity in running/ tail lights?

I bought LED replacement bulbs for interior and exterior in my 1997 Scamp 13. The interior LEDs work fine. However, the running and tail lights do not light up at all.
From reading posts on here, I deduce I have a polarity issue. My question is can I change the polarity at one single point in the wiring, or do I have to change the wiring of each individual fixture? And if there is a single point, where is it?
The battery is connected correctly black wire to positive.

Additionally and this may be a clue to the above problem, or may be a separate problem the 1157 replacement LEDs do work turn, brake and emergency flash. However, the curb side is much dimmer. I switched the two bulbs and the same thing happened its a fixture issue, not a bulb issue. And what seemed really weird to me they light up equally bright when I turn on the TV headlights. The flash function also becomes equally bright when the TV lights are turned on.

Finally, a tangential issue - Ive read the opinion that we dont need LEDs for running and tail lights because they are powered by the battery when the TV is running. Here is one situation where it would have made a positive difference. My first trip with my Scamp was January/February this year, Minnesota to Florida and back. Coming home, I ran out of gas on a freeway overpass in Illinois at night. Pulled over to the very narrow shoulder with a 30-foot drop to railroad tracks below. Huge trucks passing constantly within inches of my trailer. I had a totally inept person handling my roadside assistance call and it took her 45 minutes to locate me and get help on the way. My battery ran flat no flashers, no tail lights.
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Old 05-11-2018, 03:54 PM   #2
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You don’t have a polarity problem. You say you have brake and turn signals.
So, it’s not reversed.
You have an issue with the brown wire which feeds your running and taillights.

The dimmer light is a grounding problem. Which could be part of the problem with the running lights, no ground too them.

If your not formiliar which using a test light and or meter, you may want to take it to uhaul to find the problem.

Go to Utube , many videos on wiring and testing trailer lights.
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Old 05-11-2018, 04:08 PM   #3
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Black wire goes to negative and red wire goes to positive. Sounds like you have them reversed
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Old 05-11-2018, 04:17 PM   #4
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A 4-wire Plug is yellow, green, white and brown.
The new lights could be black and red.
They light, so its not reversed.
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Old 05-11-2018, 04:38 PM   #5
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I should have mentioned in the original post that all of the lights work as expected with the incandescent bulbs I replaced.
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Old 05-11-2018, 04:39 PM   #6
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I have a black positive and a white negative attached to the battery. (responding to Sunrisetrucker)
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Old 05-11-2018, 05:36 PM   #7
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On the house battery... Black goes to pos+ and WHITE goes to neg-

Dot wiring works separately off the TV as follows...
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Old 05-11-2018, 06:46 PM   #8
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Never rely on the color of wires at the battery. Or any other place. From the battery one wire should go to the frame (negative), the other to the converter or power distribution center if installed. You can pick up a volt meter very cheaply and no longer guess about polarity.
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Old 05-11-2018, 08:42 PM   #9
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Quote:
Originally Posted by Eggcentric View Post
Never rely on the color of wires at the battery. Or any other place. From the battery one wire should go to the frame (negative), the other to the converter or power distribution center if installed. You can pick up a volt meter very cheaply and no longer guess about polarity.
The ground wire (white)on the Scamp goes to the ground at the converter (not to the frame). The positive wire (black)supplies power to the converter and has a fuse holder in the battery box.
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Old 05-11-2018, 09:40 PM   #10
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Floyd, On the Scamp, does the converter ground to the frame? I would expect it to, have never seen a trailer that did not use the frame as ground (12v negative) Even so it is bad practice to rely on the color of a wire to determine positive or negative, a new hire at the factory could have used a different color, a previous owner may have done a repair or modification, so use your volt meter to be certain.
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Old 05-11-2018, 10:24 PM   #11
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Originally Posted by Eggcentric View Post
Floyd, On the Scamp, does the converter ground to the frame? I would expect it to, have never seen a trailer that did not use the frame as ground (12v negative) Even so it is bad practice to rely on the color of a wire to determine positive or negative, a new hire at the factory could have used a different color, a previous owner may have done a repair or modification, so use your volt meter to be certain.
Of course it can't hurt to check, especially on older trailers where mods have occurred. However, Scamp places a label above the battery box stating the color code for polarity.
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Old 05-11-2018, 11:23 PM   #12
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Originally Posted by Eggcentric View Post
Floyd, On the Scamp, does the converter ground to the frame? I would expect it to, have never seen a trailer that did not use the frame as ground (12v negative) Even so it is bad practice to rely on the color of a wire to determine positive or negative, a new hire at the factory could have used a different color, a previous owner may have done a repair or modification, so use your volt meter to be certain.
The converter grounds to the frame via the 3 wire safety ground in the power cord. The main power cord has a green safety ground wire that connects to frame.

TO THE OP.
To answer your question about reversing the polarity it will have to be done at each fixture. The tail lights and running or side light are all the same circuit, WHICH IS A DIFFERENT CIRCUIT THAN THE BRAKE/TURN SIGNAL CIRCUIT.
If none the marker lights or tail lights are coming on they are probably misswired. Get a Volt meter and check at the light if power is there. If it is the odds are that you wired them backwards.

Lessons learned, when changing marker and tail lights to LEDs change them one at time and check the light before going to the next.
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Old 05-12-2018, 12:14 AM   #13
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Floyd, a favor, take a volt meter, or circuit tester and touch one lead to the frame, and the other to the positive on the battery. I would like to know if you read 12 v (nominal) between the frame and battery.
If there is no circuit, I will study the reasoning for isolating the frame (chassis) for my own satisfaction, and so that I do not go giving out advice that has exceptions.
Thank you.
Tony.
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Old 05-12-2018, 10:06 AM   #14
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Quote:
Originally Posted by Eggcentric View Post
Floyd, a favor, take a volt meter, or circuit tester and touch one lead to the frame, and the other to the positive on the battery. I would like to know if you read 12 v (nominal) between the frame and battery.
If there is no circuit, I will study the reasoning for isolating the frame (chassis) for my own satisfaction, and so that I do not go giving out advice that has exceptions.
Thank you.
Tony.
The converter has both 12VDC and 110VAC (another subject). The converter also has a ground wire to the frame. There is 12V nominal between the battery and the frame.
I see no reason to isolate the frame from 12V house wiring nor is there a real necessity to involve it in 12V circuitry. What is the concern?
Every 12V circuit in the trailer has return to ground wiring back to the converter and thus to the battery without the need to involve the trailer frame.
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Old 05-12-2018, 11:23 AM   #15
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Floyd, Thank you for responding. I thought that would be the case, so the battery is wired negative to the frame, indirectly via the converter. No need to change anything, but where convenient you can just pick up negative from the frame, handy if it saves you running a negative wire, and of course it is electronically a massive conductor with large ampacity.
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Old 05-12-2018, 11:41 AM   #16
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Quote:
Originally Posted by Eggcentric View Post
Floyd, a favor, take a volt meter, or circuit tester and touch one lead to the frame, and the other to the positive on the battery. I would like to know if you read 12 v (nominal) between the frame and battery.
If there is no circuit, I will study the reasoning for isolating the frame (chassis) for my own satisfaction, and so that I do not go giving out advice that has exceptions.
Thank you.
Tony.
Floyd is almost totally correct. The path to the frame yes is through the converter. However that's not the end. The converter is connected to shore power and that's where the frame connection is , where the shore power enters the trailer.
REASON... I know UL requires that all metal around 120VAC items must be connected to "Safety Ground" and zero current is run in the "safety ground". The safety ground is connected to Earth at the shore power source and connected to the neutral line.
Yes you can connect a voltmeter to the + terminal and the trailer frame and find 12 VDC. WHY? Because the meter completes the loop. If current is to flow, (flowing current is what makes everything work) there must be a loop.

I hope this brief explanation helps a bit.
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Old 05-12-2018, 01:50 PM   #17
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Originally Posted by Byron Kinnaman View Post
Floyd is almost totally correct. The path to the frame yes is through the converter. However that's not the end. The converter is connected to shore power and that's where the frame connection is , where the shore power enters the trailer.
REASON... I know UL requires that all metal around 120VAC items must be connected to "Safety Ground" and zero current is run in the "safety ground". The safety ground is connected to Earth at the shore power source and connected to the neutral line.
Yes you can connect a voltmeter to the + terminal and the trailer frame and find 12 VDC. WHY? Because the meter completes the loop. If current is to flow, (flowing current is what makes everything work) there must be a loop.

I hope this brief explanation helps a bit.
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Old 05-12-2018, 07:19 PM   #18
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Nor sure how many ways there are to split this hare.
You can connect the negative battery terminal to the frame, the converter will pick up the 12 volt negative through its ground. Your the ground wire on your trailer/tow v connection connects directly to the frame, as does the battery on most tow vehicles. Both trailers that we have only use one conductor for the brakes, and uses the frame as the other.
When I install the inverter and the solar panel on our RVs (4 rv's to date) I use the frame as the negative conductor similarly with the running lights, except that since there is no frame connection available near the clearance lights we run two conductors, one of which is connected to the frame, the other to the battery +. I trust this will end this explanation which is getting a little boring.
In the mid '80's I ran a company that built enclosed trailers with any number of accessories (in those days PV was too expensive ) I trained a number of workers to wire these trailers, some with shore power, generators, A/C etc.
PS the fact that shore power ground is connected to the frame is of no consequence to the 12V system.
Thats all folks.
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Old 05-13-2018, 05:43 AM   #19
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Trailer: 13' Scamp
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Last summer I converted all (almost) all of the lights in our 2005 13" Scamp to LED and had no problems except for the marker lights. The incandescent bulbs work fine but the the LED bulbs remain dark. It sounds like the person in the original post has a similar problem. I never did come up with a solution and have the old fashion bulbs lighting the sides.
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Old 05-13-2018, 06:33 AM   #20
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On my 1978 Trillium 4500, I replaced all side markers with LED side marker fixtures. I also replaced the tail light bulbs with 1157 led bulbs. All lights worked as expected, except that every time the left turn, right turn, brake, or hazard light was switched on, all marker lights flashed on as well. Note that before I did all of the replacements, I did not have this problem and all incandescent bulbs worked correctly. I believe the reason is that in the 1157 led bulbs, there is a small current leak from the turn signal circuit to the marker signal circuit. If this is the problem, the way to fix this problem is to add a diode to the marker signal wire. I have worked around the problem by always turning on the LED marker lights while towing.

To the OP, you may have the problem I have described above and, in addition, it may be that in your right tail light, the turn signal wire and the marker wire are reversed. This second problem would explain why your right turn signal isn't as bright.

To David Uher, did you try reversing the two wires connecting to each of your side marker lights? LED bulbs have polarity and will only light up if correctly wired.
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