Trailer lights.

Hi Guys,

I am just wondering why one side of my running lights dim down, when the opposite side has the turn signal on ?

It does it when either the left or right turn signal is on .

Re: Trailer lights.

Hi N1265,
I would bet that a poor ground is the cause. You could quickly confirm this by temporarily connecting an additional wire from a known solid ground point on your vehicle to a clean spot of bare metal on your trailer light fixture(s). If you have sufficient length of wire available, you could run the wire from the body of the light all the way to the negative battery post. If this corrects the problem, you have a start on sleuthing just where the circuit has failed. Ground continuity often fails due to corrosion. What causes strange light activity when the ground is interrupted is often due to the current from a supply wire feeding a lamp filament finding no return path other than returning to the vehicle via another seemingly unrelated circuit. The relation between these circuits is the common (isolated) ground connection point between your tail light and stop/signal lamp circuit.
As long as the ground is good, each circuit operates independently in parallel, but once the ground is interrupted, current will flow through any and all paths it can find back to the battery.

Re: Trailer lights.

You must have a older tow vehicle . you most likley need a upgraded flasher as that is what make it do what yours does.

Re: Trailer lights.

another quick test is to just turn on the Emergency blinkers only. If they work correctly then its got to be the flasher. The little round thing by the fuse area under the dash normaly.

Re: Trailer lights.

Poor ground for sure.

Re: Trailer lights.

3 main causes of trailer light issues.

1. Bad ground.
2. Bad ground.
3. Bad ground.

Re: Trailer lights.

Hey guys I was hoping to find some help here too, I put on new trailer light this weekend (old ones were falling apart, bulbs breaking inside) Anyway My right blinker will not work, and everything was fine before these new ones installed. The trailer has 6 wires running to the lights (3 each side) Each new light has a ground and I ground the paint off to the metal hooked the grounds together on each side but I can't get em to blink after 2 days of trying, when I try the hazards It will not go either. The light works when you cross the wires and the fuses are fine , please help.

Re: Trailer lights.

kenmyfam said:

3 main causes of trailer light issues.

1. Bad ground.
2. Bad ground.
3. Bad ground.

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uh....so what are you trying to say???..........can you please be more to the point?

Re: Trailer lights.

I thought i was.... My right blinker will not go. I'll try some more tonight but thats it and I'm not running new wire, not this year anyway.

Re: Trailer lights.

trailersafe said:

Hey guys I was hoping to find some help here too, I put on new trailer light this weekend (old ones were falling apart, bulbs breaking inside) Anyway My right blinker will not work, and everything was fine before these new ones installed. The trailer has 6 wires running to the lights (3 each side) Each new light has a ground and I ground the paint off to the metal hooked the grounds together on each side but I can't get em to blink after 2 days of trying, when I try the hazards It will not go either. The light works when you cross the wires and the fuses are fine , please help.

Click to expand...

trailer - It's not nice to hijack a thread with your first post in a forum. Start a new thread describing your problem. BTW oops! was not responding to you, but to the quote by kenmyfan. Welcome aboard to iboats.

Re: Trailer lights.

oops! said:

uh....so what are you trying to say???..........can you please be more to the point?

Click to expand...

Can't really put it plainer than that !!!!
Unless I put it this way ......

Bad ground, Bad ground, Bad ground, Bad ground etc

Re: Trailer lights.

Sorry guys

Re: Trailer lights.

Do you have a swing away hitch? Sometimes the pivot point becomes rusted and results in a bad ground if the ground is connected to the forward portion of the tounge. The cure is to move the ground back to the aft portion of the tounge.

And of course, check all the grounds on all the lights. Clean them up, replace terminal ends, etc.

Re: Trailer lights.

I do not have a swing away hitch, I do however have a tilt trailer... Same principal I guess, as my ground wire is attached to the frame forward of the pivot point. Thanks for the tip, I will run an extra wire to the rear of the trailer.

My tow vehicle is the newest truck I got, A 1977 Dodge. surely there are no electrical issues on something that new.

Re: Trailer lights.

A ground loop is always the best way to go all the way back to the harness. Frame grounding is 99% of the problems we see here with lights.

Re: Trailer lights.

Do you run the truck side of the plug back to the battery, or frame ground the truck side ?

Re: Trailer lights.

Here is where I am at so far : I have taken the ground wires on both tail lights, spliced them together and ran a wire up to a bolt on the toung on the trailer, On that bolt is also the ground wire that comes from the trailer plug. I also have two side marker lamps that ground on the frame of the trailer and they work. I therefore believe that the trailer is grounded threw out to the plug on the trailer side.

I still have the condition of one side of the trailer light dimming down when the other side has the turn signal on, I am wondering if the problem could be :

1) the fact that the side marker lamps are grounded to the frame and do not have a seperate wire ran to the trailer side of the plug ?

2) The truck side of the plug is grounded to the frame, It looks good to me but should I run a ground wire from there all the way to the battery itself ? I do not have a problem with the truck lights and they are a chassey ground.

3) should I buy another flasher unit as suggested above ? the one I have in there now is only 3 years old, but is stock. Do I need a HD one when only running a couple of extra lights on the trailer ?

Re: Trailer lights.

N1265 said:

I also have two side marker lamps that ground on the frame of the trailer and they work. I therefore believe that the trailer is grounded threw out to the plug on the trailer side.

I still have the condition of one side of the trailer light dimming down when the other side has the turn signal on,

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I hope you've fixed the problem by now and are enjoying use of the trailer. In case you're still struggling with it, consider this:
The only connection between your side lights and your turn signal is the common ground point and a poor ground can cause this problem.
The fact that the sidelights work does not prove that the ground is as good as it should be. It is perhaps adequate only to carry the current of the sidelights. When you add the current of the signal/brake lights to the current of the sidelights, the ground path may not be adequate if it contains much resistance (eg. corroded connection point(s)). It is a mathematic certainty by "Ohm's Law" that when you increase current flow through a resistance, you proportionally increase the "voltage drop" across the resistance. You may have seen this before on a bathroom lighting circuit when someone starts a 1200W hair dryer. Even though the breaker may not be overloaded, the increased current flow causes the voltage to drop and the lights to dim slightly.
It would take very little time to run a jumper from the ground wire of your signal/brake light to the negative of the vehicle battery and prove whether the ground is bad or whether I'm full of hot air. If you don't have 40' of wire, just use an extension cord and alligator jumper from the ground pins at both ends of the cord to battery and light fixture.
If the condition disappears, start jumpering from the negative post to midpoints in the circuit until you find the bad connection.
One last point: fixing only one poor ground point may improve the system adequately for now, but fixing all the ground points and ensuring they can't corrode in the future with a little touch of grease will be a good investment.
- Grandad (electrician for 45 years, now teaching electrical apprenticeship program)

Re: Trailer lights.

Thanks for the reply, It will take me to this weekend till I am able to check it out with an extension cord, I will post the results early next week.

Many Thanks for the help...

Re: Trailer lights.

Do the lights on the truck also dim or just on the trailer? And are you talking about the tail light on trailer opposite from the flashing side?
One last one, do the marker lights dim?

I know you have been working on this for a week, don't give up. Electricity is just like water in a pipe. You have a leaky washer or joint somewhere.