Trojan LED trailer light issue

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Wheelbarrow01

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#318375 12-Jan-2025 00:26

I'm on the home stretch of a 3 month project to teardown and rebuild my flat deck trailer after a minor prang left it a bit bent.

I'll preface the post by stating that I have several trailers, all of which have LED lights, and my VW Touareg has the required load resistors to prevent the LEDs randomly flashing (I know from experience that the PX Ford Ranger also needs aftermarket load resistors to deal with LED trailer lights. PXII and PXIII Rangers had the resistors built in).

The problem is that I have just fitted brand new Trojan LED lights to my trailer. I wired them up today and plugged them in to check everything works correctly, but it doesn't...

With the engine running, the indicators and brake lights work fine, but when I turn the head/tail lights on in the car, ALL lights (including the indicators/brake lights) stop working correctly and just flash briefly in unison roughly every 5 seconds. Turn the head/tail lights off and the indicators and brake lights start working normally again.

With the engine not running but the ignition on, nothing works and I just get the all lights flashing briefly every 5 seconds (I may have to edit this line later but I think this is correct from my recollection of the day).

Incidentally, during the xmas break I borrowed a friend's trailer and had the exact same issue - I needed to drive it long distance so I ended up attaching a portable LED lightbar off my boat trailer so as not to delay the trip. Querying my friend about this further in light of today's events, it turns out his trailer lights are also Trojan brand too...

So here's what I know:

I have 3 other trailers, all with various brands of LED lights, and they all work correctly with my car.
This restored trailer with new Trojan lights, and my friends trailer with Trojan lights both do not work correctly with my car.
My car has the necessary wiring for LED lights that works with every other LED equipped trailer I own, plus a number I have rented in the past 6 years eg moving trailers, digger trailers etc.
I've double and triple checked all my wiring work including the earth return.

I guess I can call Trojan on Monday and seek help from them, but suspect they will just say I've either wired it wrong, or I need load resistors, neither of which is correct.

It's a long shot, but keen to hear if anyone else on GZ has run into this issue with their German car and Trojan lights. At first I thought maybe my load resistors had failed, but they still work perfectly with my other trailers (I checked out of pure frustration!!). If nobody has any tips, then I'll be off to the auto sparky on Monday it seems.

It's particularly annoying as these are possibly the most expensive lights you can buy ($272 a pair on the Trojan website). I specifically chose these as the piano black border matches my exquisite gloss black paint work LOL

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#3330423 12-Jan-2025 03:43

Are they dual-voltage 12/24V lights? I wonder if there's a buck converter that's throwing out noise or unexpected voltage-current curves.

Other than that, I don't really have anything other than what you've already said. Triple check wiring again (including possibility of damaged plug/socket with failing pins) and consider whether the load resistors are drawing enough current.

RunningMan

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#3330533 12-Jan-2025 09:31

2 things stand out to me:

1) Only works with engine running - suggests the slightly increased voltage from the alternator is enough to power everything, but the float voltage from the battery is too low. Possibly high resistance somewhere in the path.

2) Nothing works with the tail lights on - suggests that the others may be earthing back through the tail light circuit. Ordinarily this would be difficult with LEDs but I wonder if the recent model lights have a rectifier or similar for reversible polarity?

Combine the 2 together and it suggests an earthing problem. Perhaps grab a multimeter and check the potential difference to car battery -ve at various points and see if it is actually zero with different combinations of lights on. Open the trailer plug casing and back probe the pins while the lights are on to see what the voltages are.

If that fails, I'd be checking the light controller in the car. is it just a bunch of load resistors, or is a CANBUS controlled device?

k1w1k1d

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#3330535 12-Jan-2025 09:38

Looks like these are the 12/24v submersible marine lights.

Have fitted many LED lights from various brands in my former working life, but not sure if I have fitted those Trojan lights, so no magic cure for you.

Have you tried connecting them directly to a battery or an older vehicle without a load sensing system to make sure the lights work correctly?

Do you have a small incandescent light bulb(3-6W) that you can connect in parallel to see what happens? An old-style test light with a bulb in it would be perfect. An LED test light won't work.

Are they fitted far enough back so that they are visible for 45degrees inwards to meet NZ lighting standards?

Trojan website says they should be mounted horizontally to meet ADR requirements. Probably not an issue for an old trailer in NZ.

tweake

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#3330556 12-Jan-2025 12:12

with painted chassis, check your earths. especially the earth in the plug and how it connects to the car.

k1w1k1d

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#3330570 12-Jan-2025 12:39

These lights have an earth wire in the fully sealed loom to the plug and don't connect to the trailer chassis. They are totally electrically insulated from the trailer they are mounted on.

RunningMan

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#3330593 12-Jan-2025 14:09

Are there any LED trailer lights that are not like that? I don't recall any.

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tweake

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#3330624 12-Jan-2025 15:02

a lot of the trailer lights come with short leads, and you join it to the main lead. generally you connect the earth to the chassis at that point. that way it can use the trailer hitch as an earth if the earth pin fails. no1 failure is the pins in the plugs making a poor contact and having all the lights reliant on one earth pin means if it fails all the lights fail.

it was common just to use the hitch as the earth, but these days the plug is wired for it so its used as well.

k1w1k1d

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#3330628 12-Jan-2025 15:26

Using the hitch as the earth was always a problem with the trailer bouncing around making and breaking the earth connection. Using pin 3 on the plug has always been the correct earthing method.

SomeoneSomewhere

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#3330633 12-Jan-2025 15:49

I think they are suggesting using both in parallel. Pins in trailer plugs fail from time to time, too.

Wheelbarrow01

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#3330833 13-Jan-2025 10:56

Sorry some of the info in my original post was indeed wrong - I posted late at night several hours after my testing and I recalled incorrectly...

So I was correct in saying the brake lights and indicators work fine - together and individually - but contrary to my original post, this is true whether or not the engine is running or just the ignition is on.

But no matter whether the engine is running or not, everything fails the moment the head/tail lights are switched on.

However, if I apply the brakes while the head/tail lights are on, EVERYTHING works correctly! This is fine so long as I drive with my left foot on the brake all day LOL.

I took the advice above and used a test lamp to check all wires at the car's trailer plug (which I also recently replaced):

With the suspect trailer connected, I get no power at the tail light circuit on the car's plug. However when I unplug the problem trailer and plug in a known "good" trailer, the test light on the tail light circuit then lights up. Swap back to the problem trailer and the test light promptly goes out.

I then plugged the suspect trailer into my Senator and my Hilux, and everything works perfectly normally.

So in summary - my VW works with any LED lights except these ones, and these LED lights work with any car (or at least two others) except my VW.

There is likely some dicky issue with the CANBUS system on the VW which for some reason ONLY relates to these particular LED lights (and only the tail lights, not the brakes or indicators), regardless of the fact that the VW already has load resistors fitted.

It's got me beat, so I've booked it in with my local auto sparky for tomorrow morning.

@k1w1k1d asked a couple of extra questions - answers below:

According to the box, these lights work from 10-36 volts. Unsure if that has any bearing or not.

Yep, as above, these lights function perfectly on my Senator and my Hilux.

Re the visible from 45 degrees inboard rule - we'll see with that one. These lights are in the exact same position as prior to the prang, however I have added the diagonal bar since then to provide additional strength to the deck. The VIRM does not state at what height (if any) the lights should be visible from 45 degrees inboard. While the 25mm x 25mm diagonal bar does restrict visibility of the entire surface area of each light at various points, there is no height from which you cannot see at least some of the LEDs of each light's function from 45 degrees inboard. My father in law is a WOF and COF inspector and he says he would pass it, so I am running with that for now. The joke is that if a following motorist is looking at my lights from 45 degrees inboard, that means the front of their car has already hit me...

Mounting them horizontally to meet ADR - I don't know. I've simply replaced the old lights (which were LED by the way) with new ones in the same location and orientation. Given that the trailer is for hauling a race car, and there are lips to support the loading ramps at the rear of the chassis, there is no practical way to mount the lights horizontally at the rear without leaving them prone to hitting the ground when reversing off the road onto my property (or even speed bumps). And moving them further forward to mount horizontal on the mudguards is also not favoured as that then messes even further with the 45 degree inboard visibility rule....

Wheelbarrow01

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#3330835 13-Jan-2025 10:59

tweake:

with painted chassis, check your earths. especially the earth in the plug and how it connects to the car.

There are no earthing points on the trailer - these lights are sealed units with a white earth wire that goes directly back to the white earth wire on the car's trailer light socket. The supplementary lights (side markers) are the same - wired directly back to the main trailer plug for both positive and earth.

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gregmcc

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#3330955 13-Jan-2025 13:04

Sounds like a loading issue to me, in this case the trailer controller is seeing overcurrent and shutting down output power to all trailer lights under certain conditions, then after 5 seconds it powers back up the outputs sees the overloaded condition and powers down again.

Check the specifications on current usage for the light and do some real-world current measurements to see if they are in specification.

2 possible causes - lights are actually using too much power and the trailer light controller is shutting down, or the trailer light controller is too sensitive.

richms

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#3330960 13-Jan-2025 13:32

It will be the inrush current of the DC converter in the light if anything. Series resistance of a few ohms tends to sort it out. There will be a maximum capacitance spec on the module in the car controlling it.

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Wheelbarrow01

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#3331631 14-Jan-2025 23:29

So I went to my auto sparky today. When I showed him the problem, and also demonstrated the working LED lightbar as well, he was initially just as confused as me.

He had the car and trailer all day and ended up wiring new resistors into the trailer itself - given that the car's wiring already worked with all my other trailers' LED lamps he didn't want to mess with the car's wiring. But the extra resistors wired into the trailer now mean that everything is working perfectly. He tested the new resistors at full load for some time and observed a temperature of 60 degrees, so he's mounted them in a location on the trailer that will get plenty of airflow.

He said he had dealt with the Ford Ranger LED issue plenty of times but nothing quite like this quirky issue with this particular VW and these particular lamps. However he did state that my car wiring only appeared to have resistors on one of the light circuits (ironically the tail light circuit - the one I was having issues with for these particular lamps where all others worked fine).

Cost was $270 - more than the purchase price of the lamps ($200 on special prior to xmas). I should have just bought the uglier $75 Repco LED lamps and saved myself all this hassle and around $400. Hindsight is a wonderful thing. C'est la vie....

Wheelbarrow01

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#3336479 27-Jan-2025 23:14

For those interested, here's a link to the whole trailer build in the DIY thread...

https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=116854&page_no=61#3336477

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