Helping neighbor with trailer light problem.....

[remagenman]

Neighbor has a 2006 Toyota Highlander with OEM trailer connection in the rear. From there its connected to an aftermarket 4-pin connector that connects to trailer.

Problem is no lights when connected and turn signals/brake lights applied.

I tested the 4-pin plug coming out the truck with my multimeter and the left/right/brake work, so this is why I'm stumped at why there is no lights at the trailer.

The trailer is a basic non-braking single axle trailer.

Thanks.

 

[dcg9381]

What would impact all 3 12V signals being sent to a trailer? Bad ground.
Note turn/brake are probably 2 signals. If you have running lights, it's not bad ground.

 

[Big Bad Dad]

Make sure the 4 pin connector is wired to an actual ground on the trailer. I know some older guys used to just figure the trailer would ground through the trailer ball.... I have had to add a ground connection on a couple of old trailers in the past.

 

[mike93lx]

Yep, a ground.

Lots of trailer wiring issues are from a bad ground

 

[MarineScott]

Always check, POWER and GROUND first

 

[The Cobbler]

bad ground, bad bulbs, bad wiring in that order I would say
do you get the trailer lights to light with jumping 12volts to the plug ?

 

[kenners]

Try running a separate ground jumper wire from the trailer to the vehicle.

 

[kylefitz]

Neighbor has a 2006 Toyota Highlander with OEM trailer connection in the rear. From there its connected to an aftermarket 4-pin connector that connects to trailer.

Problem is no lights when connected and turn signals/brake lights applied.

I tested the 4-pin plug coming out the truck with my multimeter and the left/right/brake work, so this is why I'm stumped at why there is no lights at the trailer.

The trailer is a basic non-braking single axle trailer.

Thanks.

A flat four trailer connector won’t have separate brake and turn signals. Just ground, tail lights/ maker lights, left stop/turn, and right stop/turn. Like the others said, it’s probably the ground in the trailer side.

 

[remagenman]

Bought a 4 pin test light plug from Harbor Freight but have to test tomorrow, they started watching Monday Night Football! (older couple).

I'll check the ground on the trailer but they said the trailer lights work fine when connected to another vehicle.

 

[rlwhitetr3b]

The other vehicle might be grounding through the hitch while the problem one is not.

Bought a 4 pin test light plug from Harbor Freight but have to test tomorrow, they started watching Monday Night Football! (older couple).

I'll check the ground on the trailer but they said the trailer lights work fine when connected to another vehicle.

 

[The Cobbler]

does the vehicle have separate brake /turn signals?is there an adapter installed ? does their other vehicle have separate brake. turn signals ?

 

[remagenman]

does the vehicle have separate brake /turn signals?is there an adapter installed ? does their other vehicle have separate brake. turn signals ?

The car has a brake controller installed (they bought the truck that way, Tekonsha Envoy) but no light on the controller goes on. Honestly don't know if this is a cause.

 

[The Cobbler]

brake controller should not be wired in to a 4 prong trailer plug. what I was refering to is the converter that converts the European style separate signal & brake light circuits in to the North American combined signal/brake light circuit

 

[kbeefy]

The car has a brake controller installed (they bought the truck that way, Tekonsha Envoy) but no light on the controller goes on. Honestly don't know if this is a cause.

The brake controller doesn't use the 4 wire plug, so I wouldn't worry about that.
Is there a 6 or 7 wire connector in there? Thats what the Brake controller would use, and if it's functional maybe it's light circuit is also.

As mentioned, confirm a good ground on the vehicle side and that it goes somewhere on the trailer side.

 

[kbeefy]

does the vehicle have separate brake /turn signals?is there an adapter installed ? does their other vehicle have separate brake. turn signals ?

Thats a good point, the aftermarket converters fail sometimes.

But, he does have good voltage at the vehicle side plug, so that would indicate to me that the converter is working properly.
It was also mentioned that it's a factory trailer wiring harness, if so it won't need a converter. IF, in fact it is factory wiring. I recall installing trailer wiring on a LX300 or whatever the Lexus highlander is, so who knows at this point.

 

[vavet]

I battled some trailer lights problems a few years ago. All was good after I ran a dedicated ground instead of trying to use the trailer frame as a ground.

https://www.garagejournal.com/forum/threads/weird-problem-with-utility-trailer-leds.391066/

 

[jimindm]

Just use a test light between the trailer frame and the truck hitch. Turn on the lights and see if the test light lights up

 

[ycgoat]

I would remove both lights and check for continuity to ground and yo each other on all cables at all accessible locations (harness and each light. Then if all looks good, jumper the ground to each signal wire. If its a wire problem that should narrow it down. If all looks good, connect the harness to the truck and verify voltage at each light for each function.

My most recent trailer lightning problem it was intermittent. The wire insulation looked to be cracking, so I replaced the entire system.

 

[kbs2244]

no lights at all points to a lack of ground
a 20 foot spool of green wire is less than $5.00

 

[mike93lx]

no lights at all points to a lack of ground
a 20 foot spool of green wire is less than $5.00

Even better would be the white that is used for trailer grounds...green is grounding in buildings, not vehicles

 

[Leaflessshadetree]

I'm guessing ground. The other car may have better ground connection between the vehicle and the ball thus allowing the frame ground to be sufficient where this car it isn't as good of a connection.
With any trailer/vehicle you should have good ground wire connections and not rely on the ball hitch.

 

[remagenman]

Update: to everyone that mentioned "the ground" give yourself a pat on the back!

Tried the tester, power was good. Went to the ground on the trailer, cleaned it, re-applied the ground and good to go! Then the right side turn and brake didn't work but learned from ya'll that it might be the ground and yup, cleaned and worked again.

Thanks again for everyone's help and suggestions.

 

[The Cobbler]

glad you got it sorted out . I'd say in most cases trailer lighting & wiring issues is result from a bad ground