Here goes, I just purchased a used enclosed snowmobile trailer the lights are not working correctly. The trailer and top both have lights so there are a total of three bulbs for the left and right brake and turn signals, two on the top and one on the trailer.

I have a tester I plugged into the tow vehicle '07 explorer with factory tow package, the running lights, left and right turn signals and brakes lights all tested good plus it has always been fine with other trailers.

When I plug in to the trailer I have running lights but no brake or turn signal lights, I disconnected the lights on the trailer then the topper lights worked fine, I then disconnected the topper lights and the trailer lights work fine but with all them connected they won't work. I did notice after turning on the turn signals and trying the brakes with all the lights connected I then plugged in my tester and it was not working for the turn signals or brakes, I turned the key and lights off then back on and the tester was working fine again.

Sorry for the long post do you think a bad ground on the trailer and during higher current the tow vehicle is detecting a fault turning off a relay or something until a key cycle?

Thanks

 

I did one more set of tests...

1) Turned on the running lights to the trailer, let it sit for a few minutes then disconnected the trailer and hooked up the tester and everything was fine.
2) Connected back to the trailer turned on the right blinker nothing on the trailer, tow vehicle is fine, unplugged the trailer and connected the tester and the right turn and right brake didn't light. Cycled power and tested out find, did the same test for the left turn same results. Then cycled power and applied the brake, hooked up tester and both left and right were out until the next power cycle.

 

9 times out of 10 when I re-hook one of my trailers and have issues, the ground is the first place I go. It sounds like you should clean the connector first and plug/unplug several times to "clean" the contacts. I use wd-40 to help. Also, find where your ground to the trailer is and remove, clean, and re-attach to a new clean location. Most likely you will be back on the road shortly.

 

Where your tests run with the truck hooked up to the trailer? ie with the trailer hitch ON the truck ready to tow? If so, unhook it and retest...just raise the trailer OFF the truck ball. This checks to see if the trailer is using the truck grond via the ball hitch. Very UNRELIABLE ground. Should be a ground wire in the plug.

 

Yes, all test were ran with the trailer latched to the vehicle, I will try again this afternoon without the trailer connected to the ball/vehicle. I will be out of town this weekend but will post my finding before I leave.

When I return Sunday afternoon I plan to open up the 7-pin and verify/clean the the ground wire and add a second one and ground it to the trailer tongue. The trailer is aluminum and a 2001 so makes since the ground lugs being a different type of material would build up a corrosion layer between the two metals.

 

Hooked up just the light plug and same results as when the hitch was connected.

 

Checked out trailer wiring everything looked very good and clean even in the 7-pin plug. Used a battery the trailer checks out good, so now on to the vehicle '07 explorer with factory installed tow package.

I still wonder if the vehicle has an over current detection or maybe a plug that is corroded and when high current is applied to the left and/or right turn/brake wires something happens and current stops flowing until a key cycle. See post #2 With all three lights it would be drawing ~6A on both the left and right turn/brake wires.

I am going to try and get it inside this weekend and look it over. Until I figure it out I can always unplug one of the three light on each side.

 

I use a set of regular jumper cables when chasing trailer lighting problems. Make sure both ends are getting a clean connection.

If it works with the cables connected, you know you have a ground problem. Most lighting problems with trailers are bad ground or power going to ground.

 

I did some measurements and after the right, left turn or brakes trailer lights are activated there is zero volts at the vehicle connector on the pins. I got to believe there some sort of over current detection that disables the output until the next key cycle. Would like to know for sure but in the mean time I will just used the trailer with one of the three bulbs on each side disconnected.

 

When voltage goes away under load it is normally a sign of poor connections.

Steve

 

With a tow pkg set up, you should have dedicated trailer fuses under thge hood. Without voltage, it sounds like you might have blown these, probably with a bad or grounded connection as discussed.

 

Not going to rule out a bad connection but it is happening to two wires both with the same symptom, When I have seen this in the past there has always been a low voltage at the light sometime not enough to light the bulb sometimes the light is very dim.

No fuse is being blown, when I cycle the ignition power is returned for both the Right and left turn / brake lights. (for this reason I have not ruled out bad connections yet)

All the running light continue to work making me think the ground is okay

 

I get this all the time in RVs with bad connections. Whether a light is dim or lights at all usually depends on the current draw from the light or test light.

My thought regarding your hypothesis of a recycling relay is a fuse is an overcurrent device. There is no need for a recycling relay. However, if overcurrent is a concern, it is easily testable at the trailer.

Also, even if the trailer has a good ground does not mean all the lights have a good connection to the trailer ground. Once I can demonstrate the problem is not at the truck or trailer connection tracking down loose connections on the trailer itself can drive me crazy.

I am assuming you lose voltage and then, when you recycle the ignition, the load is not on the circuit and the voltage returns until you put the circuit under load. Am I understanding your situation correctly?

Steve

 

Steve - Thanks for taking the time to reply.

Your second paragraph - I did connect a spare battery I have to the trailer, I started with one set of lights at a time, first applied power to the running lights they worked as expected, then applied power to the left turn/brake, all three lights on the left side worked, then the right side, then left and right at the same time no problems. For this reason I feel the trailer wiring is okay.

Last paragraph - That is exactly what is happening, The circuit(s) left and or right will work with any two of the three bulbs in place (drawing ~4A) but not with all three (~6A)

I still have not had time to get the vehicle in side and look for connections but hope to soon.

 

Okay good, you are taking amp readings, I hate working with voltage as half the time it is almost meaningless. Now you know your bulb readings are good (I would expect roughly 2 amps per standard bulb), so you know you are not going to blow a fuse with that kind of amperage. And by using a battery and not the truck, you took the truck out of the equation. I am impressed!

Now the next place that is always suspect for me is the not the front of the seven pin plug on the truck, but the back of the plug, provided you have the standard plug that comes apart on the back side. I have often found when I open it up that some of the pins can be nearly corroded off so contact becomes weak or erratic.

If you want to verify voltage coming in on the back side of the plug and can't find a way to do it, if you have good access to the wires, you can use one of those quick connects like you normally use to connect a new wire to an existing one. Just pinch it on the wire you want to check and you have an easy port for your meter.

The reason I keep pushing the poor connection issue is every time I get stuck and go back through my work I find it always the simplest darn thing I missed that make me slap myself in the head and the "now you have power now you don't" is something I run into in RVs on slide switches and appliances on a regular basis.

Good luck,

Steve