Trailer Lights Gurus--Got a Question.

[CausticUrbanCoast]

MY 2005 Chevy has no flasher or control other than turnsignal switch, and all truck body lighting is controlled by PCM (power control module) and there is a complete set of different fuses and wiring harness (from body lights) to rear of truck for trailer lighting... Wondering if PO truck may have same setup?

Sounds like your truck had an option for towing if the harness is separate.

My F350 has the factory towing kit; the towing fuse box lives in the engine compartment on the drivers side and has harness jacks under the dash for the controller and at the end of the frame that you are supposed to utilize to prevent splicing.

For this truck, I have to have my lights on for trailer tail lights and trailer markers since that is the way Ford wired it. Brakes and signals work as they should but the police prefer the taillights and license plate light on when moving.

 

[IndyJay]

MY 2005 Chevy has no flasher or control other than turnsignal switch, and all truck body lighting is controlled by PCM (power control module) and there is a complete set of different fuses and wiring harness (from body lights) to rear of truck for trailer lighting... Wondering if PO truck may have same setup?

So you are saying that instead of a simple 12v DC circuit going to the lighting with dedicated wiring for Running , RH Sig, LH Sig and Neg/Grnd that a single wire is used with some sort of signal from the computer telling which lamps to light? Does the "complete different fuses and wiring harness" also use this computer controlled lighting instead of dedicated DC wiring? Is there a transducer available for those that have standard trailer wiring?

 

[Bearsixty7]

So you are saying that instead of a simple 12v DC circuit going to the lighting with dedicated wiring for Running , RH Sig, LH Sig and Neg/Grnd that a single wire is used with some sort of signal from the computer telling which lamps to light? Does the "complete different fuses and wiring harness" also use this computer controlled lighting instead of dedicated DC wiring? Is there a transducer available for those that have standard trailer wiring?

Most pickup's today have similar, The on board computer may control the signals but they still go through 7 individual wires.
There is a set of fuses that the signals go through before going to the trailer connector receptacle at the back of the truck. This way if there is an issue with the trailer lights or wiring, it only blows those fuses and the pickup's lights are still fully operational.

 

[IndyJay]

Most pickup's today have similar, there is a set of fuses that the signals go through before going to the trailer connector receptacle at the back of the truck. This way if there is an issue with the trailer lights or wiring, it only blows those fuses and the pickup's lights are still fully operational.

Understood, but DLM said that if his "truck lighting is controlled by 'computer' (ECM/PCM/BCM) getting trailer lamps to work is whole different ball game than a non computer controlled (old school) system"....

I was wondering how this changed how you troubleshoot trailer lighting.

 

[aczlan]

Understood, but DLM said that if his "truck lighting is controlled by 'computer' (ECM/PCM/BCM) getting trailer lamps to work is whole different ball game than a non computer controlled (old school) system"....

I was wondering how this changed how you troubleshoot trailer lighting.

On the trailer its the same, at the back of the truck its the same the only difference is that the computer turns power on and off vs a switch, a relay and a flasher module. More reliable, but when the computer fails, then it gets expensive in a hurry.

Aaron Z

 

[WranglerX]

So you are saying that instead of a simple 12v DC circuit going to the lighting with dedicated wiring for Running , RH Sig, LH Sig and Neg/Grnd that a single wire is used with some sort of signal from the computer telling which lamps to light? Does the "complete different fuses and wiring harness" also use this computer controlled lighting instead of dedicated DC wiring? Is there a transducer available for those that have standard trailer wiring?

Correct... BUT no transducer needed... All truck does is supply a different path for all lamp & brake functions to trailer than the paths to lamps on truck body.... Trailer wiring always stay the same...

 

[WranglerX]

Most pickup's today have similar, The on board computer may control the signals but they still go through 7 individual wires.
There is a set of fuses that the signals go through before going to the trailer connector receptacle at the back of the truck. This way if there is an issue with the trailer lights or wiring, it only blows those fuses and the pickup's lights are still fully operational.

Correct...

 

[WranglerX]

Yeah, i have not seen this trailer frame grounding thing. Must be something new. But i can see the benefit of ground to trailer frame as long as the white wire is "also" run back to the tow vehicle frame through the connector.

Way back in dim times (around 1954) many trailers used to ground frame through coupler and ball.... Having intermitted success keeping lights working.... My father being the sharp person he was actually connected a wire to trailer frame and uses huge alligator clip on other end to clamp on tow vehicles frame.... As a very young lad I learned something there... This was before it was really popular to include ground wire in trailer wiring harness/connectors...

 

[WranglerX]

On the trailer its the same, at the back of the truck its the same the only difference is that the computer turns power on and off vs a switch, a relay and a flasher module. More reliable, but when the computer fails, then it gets expensive in a hurry.

Aaron Z

Yeah.... PCM was $365 plus labor... And it did not fail towing, truck was running fine and parked in drive way, shut it off and when inside, next morning went to start it up and NOTHING worked properly.... As a side note PCM only has 2 clips and two large plugs, it physically can be changed in about 10 minutes.... Killer situation is the PCM has to be programed with vehicles VIN number or it wont communicate with other modules, and programing can only be done at dealership unless you want to spend $2500-3000 for all the programing hardware/software...

 

[CoyPatton]

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

To further clarify this (at least for me)!
Your turn signals (green and yellow wires) should be energized when the turn signals in the tow vehicle are activated. Brake lights should be activated when breaks are pressed (energizes the green and yellow wires, turn signal is primary function. Meaning blinker will work on that side over brake light). Tail and marker lights (brown wire) are only energized when tow vehicle lights are on (regardless of auto lights or not).
If wiring is correct, then ground is your issue. Many 12 volt electrical issues are ground related. A lot of the time the trailer frame does not provide a consistent ground due to rust. If ground is dependent on the ball/hitch connection, a faulty ground is a given!

 

[JWR]

Oh nonsense !! There is obviously no ground problem since at times he has trailer lights. Secondly the trailer lights work just like the truck -- when he has truck lights and/or ignition on.

Conclusion: There is no problem and there was no problem in the first place.

 

[npalen]

Oh nonsense !! There is obviously no ground problem since at times he has trailer lights. Secondly the trailer lights work just like the truck -- when he has truck lights and/or ignition on.

Conclusion: There is no problem and there was no problem in the first place.

The only problem was the guy wiring the new trailer lights if you're referring to me as the OP but that was taken care of with a little help from my friends here at TBN. Remember the lyrics "I get by with a little help from my friends"?

 

[charliecrew]

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Installed these lights on my little utility trailer and everything works correctly except the tow vehicle lights have to be on for any trailer lights to work.

That wasn't the case with the old trailer lights and everything works correctly on the pickup to which the trailer is attached.

I suspect this issue is related to the fact that the '03 Dodge Dakota doesn't have automatic lights, the switch has to be turned on manually.
I can live with this but wondering if there is a way "around it"?

TIA for any comments.

The trailer lights mirror the tow vehicle lights. If this is what ic happing it is nonmail.

 

[JohnInLoudon]

Amazon.com: iBrightstar IP68 Waterproof Square Trailer Lights kit, Red Brake Stop Tail Running License LED Light Lamp for 12V Camper Truck RV Boat Snowmobile Marine Under 80", DOT Compliant: Automotive

Buy iBrightstar IP68 Waterproof Square Trailer Lights kit, Red Brake Stop Tail Running License LED Light Lamp for 12V Camper Truck RV Boat Snowmobile Marine Under 80", DOT Compliant: Tail Light Assemblies - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

smile.amazon.com

Installed these lights on my little utility trailer and everything works correctly except the tow vehicle lights have to be on for any trailer lights to work.

That wasn't the case with the old trailer lights and everything works correctly on the pickup to which the trailer is attached.

I suspect this issue is related to the fact that the '03 Dodge Dakota doesn't have automatic lights, the switch has to be turned on manually.
I can live with this but wondering if there is a way "around it"?

TIA for any comments.

It's a good trouble shooting plan to cut the problem in half by determining whether the truck r the trailer is the problem. This tester will do that Amazon.com: SeaSense EZ TROUBLESHOOTER Circuit Tester: Sports & Outdoors

Just plug it in and cycle through parking and brake lights. The LEDs will tell you where you have power.
A multimeter can also work if you have one, or this ( Premium LED Bulb Automotive Circuit Tester, 6-24V Test Light with 135 Inch PU Extended Spring Wire, Sharp Hard Steel Probe Vehicle Circuits Low DC Voltage Light Tester: Amazon.com: Industrial & Scientific )

Or, try connecting the truck to another trailer, or the trailer to another truck.

You wrote that the previous lights worked without manually turning on the truck lights. Did this truck come with factory installed trailer lighting? If so the trailer lights will reflect the status of the truck's lights. Were the earlier trailer lights the same type as the current lights (wattage, LED, incandescent) ? If the truck trailer wiring was aftermarket the wire connections are highly suspect.

BTW: A standard 4-wire trailer connector has a ground wire, a tail light-running lights wire, a left-hand brake/directional light wire, and a right-hand brake-directional light wire.

 

[ljjhouser]

Thanks. I will give that a try. I guess the confusing part is the white wire on the trailer harness at each light location. This, to me, is ground or neutral but your comment earlier leads me to believe that the wire wire is actually is a substitute for brown for the tail lights. (running light) Then the second wire (black in my case) of the trailer harness would go to the yellow wire on the left side and green on the right side.

You mentioned the term "neutral." That may make this confusing. There is no neutral, only ground in a simple trailer wiring setup such as this. Most people associate a neutral wire with the white wire on 120v circuits. Those circuits can have both neutral and ground. They may or may not terminate at the same block in the entrance panel. I am glad you finally got it solved. best wishes, Larry

 

[ljjhouser]

Hopefully, wiring all lights to a ground wire connected to a single point means you only need to check the single point where the wire is grounded (ground wire to connector) to solve a ground problem. And if the connections are soldered and sealed, that will be the only place to check for grounding problem on the trailer. And if only one or two lights fail, You will know it is not usually the ground. If they are all out, check the ground point. If you ground to the frame, you may continue to have problems with separate ground problems with random lights.

 

[Bob Rooks]

Do you mean brake lights don't work unless headlights are on? I'd check your truck on a different trailer and check the trailer on a different truck.

I do know newer Fords sometimes have problems with low impedance LED lights. The "smart" brake controller isn't smart.

Also, it could be ground. Run a ground wire externally to each light in turn to verify. On my trailer, I ended up with an intermittent problem. Eventually I figured out a ground problem. Its a tilt trailer and the trailer harness was grounded to the tongue and the lights to the frame. The frame/tongue pivot is old and corroded. The fix was a ground jumper at that location.

Many Fords do not have a flasher unit. My '08 F350 turn signals are controlled by the ECM. Found that out when I went to install LED's. Have to use external resistors on all four corners, but that also compensates for LED trailer lights.

 

[bcp]

Do brake lights still work with ignition off?

Bruce

 

[WranglerX]

It the end it is just a "current loop" with electrons flowing from source (generator/alternator/battery) then trough "lamp" (incandescent/LED) and then though "switch" (headlamp/turnsignal) and back to source... To confuse the issue electron flow is from negative side power source to positive s

ide of power source...

 

[bcp]

To confuse the issue electron flow is from negative side power source to positive side of power source...

It makes sense as the negative side is losing electrons while the positive side is gaining electrons.

Bruce