# Trailer lights acting funny



## Leah Frances (Jan 13, 2008)

The lights on our small class 1 trailer are acting funny. 
Symptoms:
-Left side rear light does not ignite when the car is 'on' (right side ignites - running lights). 
- When the brakes are engaged the left side light ignites, but only to the level of the running lights - not 'bright' like the right side.

Ideas for how to troubleshoot this?


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## jomama45 (Nov 13, 2008)

99% odds it's a grounding problem. :thumbup:


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## Leah Frances (Jan 13, 2008)

Yeah, figured that one all on my own. I just don't know how to troubleshoot it to find where the fault is. Thoughts?


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## jomama45 (Nov 13, 2008)

Some trailers are grounded thru the vehicle hitch, so you can try wirebrushing the hitch ball first.

If that doesn't work, check for a loose white wire @ the trailer tongue or at the left rear tailight.

If that doesn't work, check the white wire at each taillight & running light.

If all of that doesn't work, check all the wires to make sure they didn't wear thru, especially at penetrations.


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## Yoyizit (Jul 11, 2008)

Post a schematic; we'll step you through it.
You can use clip leads and the vehicle battery to check the trailer lights separately from the vehicle.

This lamp or equivalent used?

#1034 MINIATURE BULB BAY15D BASE - 12.8/14.0 Volt 1.80/0.59 Amps S8 Double Contact (DC) Index Bayonet (BAY15d) Base 200/5000 Average Rated Hours 2.00" Maximum Overall Length #1034

A bad ground will cause the thick filament to supply current to the thin filament, but the thick one doesn't light while it's doing this.


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## Leah Frances (Jan 13, 2008)

I'll put something up - just for giggles it appears that they coated all the wires black with some sort of paint.


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## kenmac (Feb 26, 2009)

If the bulbs are 1157 type Check the bulbs for corrosion at the terminals.. I replaced the lights on all my trailers with the LED style... Now I have o light problems


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## Thurman (Feb 9, 2009)

I've wired many a trailer, tag-a-longs, fifth wheels, boat, utility, cargo, and car hauler trailers. One thing I've learned to do to save me or someone else problems down the line is to use the white grounding wire(s) starting from the tow vehicle all the way to each light set. I just do not use the trailer framing or the hitch ball as the ground. Make a good ground on the tow vehicle if there is not one and carry it through the connector. Ground problems are probably about 95% of trailer light problems. Good Luck, David


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## brokenknee (Dec 13, 2008)

Is this problem specific only to this trailer? The first check would be on the tow vehicle. You can purchase a test light that plugs into your trailer light connection for only a few dollars. Most problems I have had with trailer lights either is a ground on the tow vehicle or problems in the connector itself.


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## Leah Frances (Jan 13, 2008)

Reality check - I'm used to house electrical so 12V DC is a strange new world. There are only two wires that run to each light. One is 'hot', right? The other is the 'ground/neutral'? If I run another 'white neutral' do I use it in lieu of the ground/neutral? In addition? 

The wires running into the lights are both the same colored wire.


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## jomama45 (Nov 13, 2008)

Leah Frances said:


> Reality check - I'm used to house electrical so 12V DC is a strange new world. There are only two wires that run to each light. One is 'hot', right? The other is the 'ground/neutral'? If I run another 'white neutral' do I use it in lieu of the ground/neutral? In addition?
> 
> The wires running into the lights are both the same colored wire.


 
Nothing like residential wiring. If I remember correctly:

White = ground
Brown = tailights/running lights
Yellow = left turn
Green = right turn 

So, you should have a brown & yellow going to left tail, & brown & green going to right tail, theoreticaly. I would take a closer look at the left tailight , as it has to be grounded through the frame some how. I'm sure it too rusty/corroded to make a good ground.


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## Leah Frances (Jan 13, 2008)

Connection (ground) is established through the bolt that fastens the light to the trailer. I will check to make sure the connection is good and free of corrosion. FYI, the trailer is less than 1 year old.


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## Yoyizit (Jul 11, 2008)

Nobody ever died from 12v in the conventional sense so Hot and Neutral kind of lose their meaning, along with the wire colors.


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## Leah Frances (Jan 13, 2008)

Each side light has two wires going to it. White wire seems to terminate at the ball. If I want to run a separate neutral/ground what would I hook it up to at the light end. Each light has two terminals - where would I attach the white?


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## kenmac (Feb 26, 2009)

If you have the 4 prong plug .The w from the plug will have to tie into both whites at the lights that wat you are directly grounded to the lights.. Not grounding through the trailer frame


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## 47_47 (Sep 11, 2007)

Leah Frances said:


> Each side light has two wires going to it. White wire seems to terminate at the ball. If I want to run a separate neutral/ground what would I hook it up to at the light end. Each light has two terminals - where would I attach the white?


The ground connection is the lamp housing. I'd put a ring terminal on your new ground wire and put the terminal between the head of the bolt and the housing.

Added: Automotive (trailer) wiring is suspect to corrosion. Get the shrink style ring terminals.


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## Yoyizit (Jul 11, 2008)

Looks like there are several wiring methods out there
http://images.google.com/imgres?img...m&hl=en&safe=off&client=safari&rls=en-us&um=1


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## Leah Frances (Jan 13, 2008)

Cool. I've got a spare spool of brown bell wire I can use to do the neutral/ground. 

Just kidding. :laughing: White wire it is!


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