Trailer Light Frustration

[hriehl1]

1999 Honda Odyssey with an OEM 4-pin extension plugged into the car's built-in pre-wired trailer-light takeoff (behind left rear trim panel near taillight). A 4-Pin test device and a circuit tester both indicate all 3 functions (brake, tail and turnsignals) work correctly at the plug where the trailer connects.

I have tried 4 different trailers whose lights I know are good and on every one ONLY the tailights work... no turn signals and no brake lights. Yet the tests on the carside plug indicates all functions work OK.

I have rewired, I have emory-clothed all connections to their shiniest... all to no avail. I know most problems are related to grounds. Could there be enough of a ground to light a single LED on a trailer light test-plug, and flip a needle on a circuit-tester.... but NOT be a good enough ground to light a lamp? Does it make sense that taillights work, but brake lights and turn signals do not?

I read in another thread where one should test trailer lights off of a battery charger... that's next. But if anyone has other ideas, I'm all ears.

Many Thanks

 

[nuttyboater]

Re: Trailer Light Frustration

I've dealt with this stuff hundreds of times before, lets take one step back...

You said testing the vehicle's trailer plug everything checks out, but does your check light actually flash on and off when turning on the vehicles turn signal?

Green is Right Turn Signal and Stop
Yellow is Left Turn Signal and Stop
White is Ground
Brown is Marker and Tail

The problem with newer vehicles is they have a seperate circuit for the stop and turn lights, in the old days all vehicles were wired the same as the trailers. Now days you need a converter to combine the stop and turn circuits.

Put your test lights ground lead on the white wire on the vehicles four pin trailer plug, then turn on your left turn signal and make sure just the Yellow wire is powered and flashing on and off, this is the first check i make. This tells me the ground is good and the wiring is correct, of course also check the Green with the right turn signal on. Then have someone hold down the vehicles brake pedal or just a stick and wedge it against the front of seat, don't laugh i've had to troubleshoot this stuff by myself a lot, and with the brake lights on again turn on the left or right turn signal and again check the Yellow and Green wires for a pulsing on and off with your test light.

If all this checks out then the vehicle is wired correctly, on to the next step.

Since you said this happens with more than one trailer i'm almost convinced that your problem is on the vehicles side, but i'll continue.

Now plug in to the trailer wiring, but DO NOT have the trailer connected to the vehicle in any other way, don't have the coupler on the ball or the safety chains connected, the goal is that the trailer and vehicle are not touching in any way except through the wiring, this will check that the ground from the trailer side of the wiring harness is bonded to the frame and working correctly. I have seen it where the ground comes loose on the trailer side and the lights are intermittent because its getting a ground through the ball hitch or the safety chains.

This also depends on your style of wiring, some trailers i have dealt with actually have the white wire running to each light, but the most common is to have the white wire bonded to the trailer frame and each light's ground wire is bonded to the frame by use of one of the mounting screws.

 

[nuttyboater]

Re: Trailer Light Frustration

One more addition to this..

Everyone seems to get confused on these converters..

Your trailer uses a 4 wire system which combines the turn and stop to the same brighter filament of the bulb in your rear lights, this is the way vehicles used to be, it turned on both for brake and flashed either one for turn while the brakes were/were not also applied.

Left Turn - Stop
Right Turn - Stop
Tail
Ground

Newer vehicles use a 5 wire system in which they seperated the brake and turn circuits to seperate bulbs.

Left Turn
Right Turn
Stop
Tail
Ground

The converter takes the vehicles stop/brake output and powers both of the turn signal wires to the trailer, or the brighter element in the bulb, for the brake lights, and flashes either of them for a turn signal.

 

[john from md]

Re: Trailer Light Frustration

If you don't have a towing package, you need to buy a five to four converter. These are about $25 in Pep Boys, Advance Auto and West Marine. Hook it up and your problems will disapear.

John

 

[stevenw00]

Re: Trailer Light Frustration

I'd have to lean towards a ground issue on the trailer. My trailer gets its ground through the ball, and until we did some scuffing on the ball and inside the coupler I had to use jumper cables between the trailer and truck in order to get a good enough ground.

 

[hriehl1]

Re: Trailer Light Frustration

Thanks for the thoughtful replies... I'll try out your procedures tomorrow night (my next free time to get after these %$#@& lights).

 

[Silvertip]

Re: Trailer Light Frustration

Trailer ground should NEVER be made through the coupler ball since it is simply not a good ground. That's what the ground wire in the connector is for. As for the Honda wiring, a converter is necessary ONLY if the stop and turn signals are on separate bulbs. On some vehicles this is obvious since the turn signals are amber. Other vehicles like the Mopar Minivans, you have to look pretty close to determine if the stop and turn signals are really separate bulbs. If you connected four trailers and none of them work, the trailer is not the issue. You apparently need a converter for the reasons previously indicated.

 

[CATransplant]

Re: Trailer Light Frustration

The OP said that he had an OEM connector on his Honda. To me, that means a factory install. I'm betting that that vehicle has separate stop and turn lights, so there's probably a converter already wired in. I'm also betting there's a problem with that converter. Maybe a bad ground in it. It passes enough current to light the LEDs on the tester, but not enough to run the trailer lights.

Sounds like a trouble shooting job for the dealer, to me. Who knows where that adapter is located. It could even be part of the OEM lighting module somewhere on the vehicle.

 

[DRIFTER_016]

Re: Trailer Light Frustration

The OP said that he had an OEM connector on his Honda. To me, that means a factory install. I'm betting that that vehicle has separate stop and turn lights, so there's probably a converter already wired in. I'm also betting there's a problem with that converter. Maybe a bad ground in it. It passes enough current to light the LEDs on the tester, but not enough to run the trailer lights.

Sounds like a trouble shooting job for the dealer, to me. Who knows where that adapter is located. It could even be part of the OEM lighting module somewhere on the vehicle.

It's located behind the plastic trim on the drivers side in front of the left side tail light. (my dad has one)

You can always reground the white wire to the chasis as there is about 4 feet of wire between the converter and plug.

 

[nuttyboater]

Re: Trailer Light Frustration

If it is indeed a factory installed converter then he should be ok but thats not to say that something isn't working correctly yet.

Another thing i have seen a lot of is the Hoppy style harness, where you unplug the vehicle harness behind the panel in the same location and put the "T" connector of the Hoppy harness inbetween. But it still uses one of their converters also.

Another thing to try to troubleshoot if its a ground problem, build or buy a jumper lead with alligator clips, its good for checking stuff like this and an essential in my toolbox.

If nothing else grab some jumper cables and put one end on the vehicle frame and the other on the trailer frame, scratch them around a bit to make sure you get a connection to bare metal.

And you can also take a continuity tester and check from the white wire on the vehicles plug to the vehicles frame.

Just test, test, and test some more. Only way to narrow it down.

 

[hriehl1]

Re: Trailer Light Frustration

Well... I got it. Of course, in retrospect, it was obvious.

I had bought a combination dongle from some internet trailer place that plugged-in to the Honda's proprietary-connector trailer-light take-off behind the rear trim panel.... that OEM take-off was 5-wire and the dongle also (was supposed to) convert the setup to 4 wire.

I put a volt meter on the dongle output and got 11+ volts for the taillights, but only 3 or 4 for the brake and turnsignal lights. I replaced the faulty 5-wire to 4-wire black-box converter portion and all is OK now.

Morals of story.

1. Those little LED testers will light up with 3 volts when a trailer lamp won't. Don't be misled.

2. When putting a voltmeter on the circuits, don't just casually look to see you're getting some volts... look closely at how many volts.

Thanks all for your help.

 

[CATransplant]

Re: Trailer Light Frustration

I'm really glad you got it working.

 

[12vMan]

Re: Trailer Light Frustration

Yey, merrily

Always good to see the light bulb light up (no pun intended)

 

[nuttyboater]

Re: Trailer Light Frustration

Just for curiosity sake, what brand was the adapter you bought? The only one i can find available for that make/model vehicle online is a Hoppy brand, of course thats also rebranded to a few other names as well.

I assume you paid a little more and got a better converter box to go inline the second time around, been there done that, i know how it goes.

On another note...

If anyone has a Pontiac Transport/Montana, or the Venture, with the towing package from the factory they don't always have the converter and trailer plug, but there is always the factory plug by the air compressor for the rear suspension. I bought a powered converter and cut off the factory plug since it was too expensive to get a matching connector for it, and just used those 3m heatshrinkable splices, the waterproof ones with the hot melt glue inside.

There is all the wires you need plus a fused supply at that plug, so with a seperately powered converter you don't need to run a lead to the battery and you have a factory fuse in the underhood distribution panel for it! Bonus and kudos to Pontiac/Chevy for adding that!

 

[hriehl1]

Re: Trailer Light Frustration

I do not know the brand of the original dongle I bought... the one that fit the proprietary Honda connector AND (supposedly) converted 5-wire to 4-wire.

I kept the connector portion and cut-out the faulty black-box 5-wire to 4-wire converter portion and replaced it with a 5-to-4 converter from Wal-Mart for $14. Works fine now.