Trailer Lights dark when headlights on

[jtexas]

Re: Trailer Lights dark when headlights on

I think I may have this thing narrowed down, but would like your guys confirmation. I am getting a DC volt reading on the green, yellow, but not the brown wire. Is that the problem, the fact that the running lights aren't working related to no juice feeding from the brown wire from the vehicle? Is this the problem.

Yes, that's the problem. I guess you may have already did this, but check your vehicle fuse chart - may have a separate fuse for that circuit.

 

[raylab]

Re: Trailer Lights dark when headlights on

I'm interested in seeing the fix on this one. My bet is a bad or weak ground. If the rest of the lights work UNTIL you turn on the vehicles running or headlights that further indicates a weak ground. The trailers running lights add a constant load thus are more susceptable to a bad ground. In the case where StudlyMandingo is presenting the difficulties of trailer wiring, I again go back to the ground. Keep it clean and keep a good contact and 99.99% of the wiring problems will be resolved. Like SilverTip I too have had trailers (utility not boat) wired for years without any problems. You just have to follow ALL the rules and keep the grounds clean, keep the contacts clean (plugs n receptacles) and keep the bulbs dry. K.I.S.S. really wirks here...

Ray L

 

[Motor Boater Bill]

Re: Trailer Lights dark when headlights on

I'm quoting myself from another post on LED lights:

As far as grounding wires, remember that the lower the voltage, the less resistance the circuit can tolerate. Consider this--the coil in your ignition generates super high voltage so it will jump a spark plug gap--talk about overcoming resistance! So with only 12 volts in your trailer lighting system, it doesn't take much corrosion on the ground side of the circuit to make it dim or dead. I've had good luck solving problems by running supplemental ground wires on trailers.

 

[rottenray6402]

Re: Trailer Lights dark when headlights on

I'm betting on a blown fuse that feeds the tail light circuit of the Trailblazer.

 

[bruceb58]

Re: Trailer Lights dark when headlights on

This is not true.

It is current across the resistance which causes a voltage drop. LED lights can tolerate a higer resistance because the current is lower.

I'm quoting myself from another post on LED lights:

As far as grounding wires, remember that the lower the voltage, the less resistance the circuit can tolerate. Consider this--the coil in your ignition generates super high voltage so it will jump a spark plug gap--talk about overcoming resistance! So with only 12 volts in your trailer lighting system, it doesn't take much corrosion on the ground side of the circuit to make it dim or dead. I've had good luck solving problems by running supplemental ground wires on trailers.

 

[klicknative]

Re: Trailer Lights dark when headlights on

I'd say the best way to isolate the problem is to get one of the LED testers that plug into the pigtail on the tow rig. If that checks out OK, the problem is most likely in the tail-marker circit (brown wire) on the trailer. An ohm meter is the most reliable way to check that. If that checks out OK, then it's a grounding problem. A common sign of a bad ground is the turn/stop lights work fine with the tail lights off but only one side lights up and all the other lights go dark when you apply the the brakes with the tail lights on.