Trailer Lights Gurus--Got a Question.

[npalen]

I think with all comments and things considered, the issue is no power to the trailer unless pickup lights are on.
The brown wire in the pickup's trailer connector will not show 12 volts unless the pickup lights are turned on.

I'm thinking now that the issue is the aftermarket trailer light plug-in adapter/harness that plugs into the pickup's light harness. It will only send power to the trailer if the pickup's lights are on.

I'm thinking now that the old trailer lights couldn't have worked either unless the pickup lights were on.

 

[npalen]

With a 4pin connector the taillights and signal lines are only energized when the vehicle's are.

Whatever the vehicle behavior is will be what your lights are: so if your vehicle has no markers unless the headlights are on, the same goes for the trailer

But the blinkers and hazards etc should work even if the pickup lights are off. (Ignition on) Right?

 

[npalen]

Edit: I knew this topic had the potential for an interesting discussion but I'm starting a headache.

 

[CausticUrbanCoast]

But the blinkers and hazards etc should work even if the pickup lights are off. (Ignition on) Right?

Blinkers should, hazards if they are wired that way, and none of the fuses are blown or trailer wires shorting.

The flat 4,5,6 and 7 should all have brakes combined with turn signals if you follow standard wiring.

The round 4 connector is not specified that way that I know of.

 

[herm0016]

it sounds like the ground is being switched by turning on the headlights somehow. get out your meter and test the polarity of the voltage from the ground in the plug to the one of the other pins with that pin on ( lights or whatever) i'm thinking it was wired backwards. an incandescent lamp does not care about polarity, and an LED does. so that could be the source of the difference be behavior. just a thought, as its an odd issue.

 

[npalen]

it sounds like the ground is being switched by turning on the headlights somehow. get out your meter and test the polarity of the voltage from the ground in the plug to the one of the other pins with that pin on ( lights or whatever) i'm thinking it was wired backwards. an incandescent lamp does not care about polarity, and an LED does. so that could be the source of the difference be behavior. just a thought, as its an odd issue.

Double checked the polarity and it is correct.

 

[CausticUrbanCoast]

DOT is dumb with lightning requirements, it is only recent that taillights were added to the daytime lighting requirements.

If your trailer light bulbs are of the dual voltage type, they expect your markerlight/headlight switch to be on. This provides a low voltage power to your trailer lights for the 4pin connectors. It was a cheap way for companies to provide the function without extra wiring.

You will only see 12V on the line if fully energized by the brakes or signal pulse. Otherwise if the marker/headlights are on you will see somewhere between 5-9V if I recall.

As a side note: this behavior will vary slightly depending on if your trailer wires were connected to the front or rear wires.

 

[npalen]

Bear in mind again that there is no power to the 4pin trailer connector UNLESS the pickup lights are ON. The trailer lights all work perfectly then.
Nothing can work if there is no power. The issue has to be in the pickup wiring, right?

 

[Doughknob]

Sounds to me like the truck's trailer wires are not connected properly. Does the same truck hooked up to a different trailer, work properly?

 

[flyerdan]

I would test the plug on the pickup with a DMM and see if it got the same signal that the vehicle lights did, that should isolate the issue.
You can also test the trailer with a 12v source (like an old power supply from a computer, who doesn't have a few of them around) and confirm that they work as they're supposed to.