LED Trailer Light Frustration - Add Loading Resistors

Denver Tom

New member
I need some suggestions for what to try next...

2008 ERA 2500
Factory wired trailer kit
7 pin round socket
Professional LED trailer light tester at the socket (so trailer wiring eliminated as culprit)
All lights on rig functioning correctly, with no dash error messages

Left signal flashes, but is dim
Right signal returns a rapid flash, almost flutter
No brake lights

I started at the rear and confirmed that all connections at the socket are solid and corrosion-free.

I traced the harness along the frame rail to make sure there is no damage. None apparent.

Driver's seat removed, integrity of harness into Trailer Light Converter checked.

All fuses under dash checked for continuity.

Trailer Light Converter swapped on the hunch that it had failed. Did not alter the results.

Now I'm at a loss for what to check next.

We trailered for many years without any issues. This came out of the blue several weeks ago.

We are in Denver, so not really prone to corrosion, though we have been at the Gulf and Atlantic a number of times.

I'm open to any suggestions that you all might have.

Thanks in advance!!

Denver Tom
 

sailquik

Well-known member
Re: Trailer Light Frustration

Denver Tom,
What "Trailer Light Converter swapped on the hunch that it had failed. Did not alter the results".
The trailer light convertor on the rail in the driver's seat box......or something else.
Do you have a VOM....are you getting 12 VDC at the pins in the 7 way round connector on the
rear of your RV.
Have you ohm'd out the ground to the ground pin in the connector on the back.
Is the trailer you are going to use equipped with incandescent bulbs or LED's?
Do you have a trailer brake controller hooked up?
Hope this helps,
Roger
If you have the MB OEM factory trailer connector there should be a schedule of what wire does what on
the flap/cover.
 

Denver Tom

New member
Re: Trailer Light Frustration

Sailquik -

Thanks for the quick response!

Yes to OEM Trailer Light Converter installed on the rail under driver's seat. That is the one I checked and swapped - which did not correct my issue.

Pro tester and trailer are both LED, not incandescent. The trailer lighting did work fine for the last 6 years with Sprinter/LED on trailer combination.

No electric brake controller hooked up, as loaded trailer 1,500 lbs max.

If I read between the lines, I think your hunch is a grounding issue.

I'll grab the VOM today and ohm-out the ground, as well as verify DC voltage.

Now that I think about it, I did recently have a genny starting issue that was the result of a lost ground.

Thanks again for your advice. Electrical bugs always give me a migraine!!!

Denver tom
 

sailquik

Well-known member
Re: Trailer Light Frustration

Tom,
It was just a guess, but RV's (with all the wood and composite rear body work) seem to have a lot of rear grounding
issues.
Might be worth it to run a #10 or #12 AWG ground wire from the main chassis ground in the seat box or
on the firewall back to the trailer receptacle and a jumper to the steel hitch assembly.
Then your trailer can ground through the hitch or through the dedicated ground pin in the trailer connector.
Solder/shrink the connections, and you won't have any further grounding issues.
Hope this helps,
Roger
 

220629

Well-known member
Re: Trailer Light Frustration

Is the LED trailer new to your rig or has it worked properly in the past?

There have been posts here indicating that LED trailer lights can have issues with the OEM trailer harness option. The incandescent lamps provide more load so are a bit more forgiving for any monitoring the computers do.

Do you have access to a trailer with conventional incandescent lamps? It might be worth backing up to it for a quick real world test.

:2cents: vic
 

lindenengineering

Well-known member
Re: Trailer Light Frustration

Is the LED trailer new to your rig or has it worked properly in the past?

There have been posts here indicating that LED trailer lights can have issues with the OEM trailer harness option. The incandescent lamps provide more load so are a bit more forgiving for any monitoring the computers do.

Do you have access to a trailer with conventional incandescent lamps? It might be worth backing up to it for a quick real world test.

:2cents: vic
Yes Vic
I have experienced two incidences of this freak out when connected to U Haul Trailers with LED lighting.
Always something to be aware of!:cheers:
Dennis
 

Denver Tom

New member
Re: Trailer Light Frustration

Aqua Puttana and Dennis -

Bingo!

LED trailer lights had worked for the past 5 plus years, but the Sprinter suddenly decided it no longer likes them.

Thanks for all the great suggestions.

I tried them all, then finally plugged in a set of "magnet" style incandescent trailer lights.

All issues suddenly disappeared.

Now I need to either replace the LED trailer lights on the boat trailer, or perhaps more appropriately, figure out how to create enough resistance so that the trailer works again with the Sprinter.

Hey, at least it wasn't the boat that broke this time!!!

Denver Tom
 

220629

Well-known member
Re: Trailer Light Frustration

...

I tried them all, then finally plugged in a set of "magnet" style incandescent trailer lights.

All issues suddenly disappeared.
...
Denver Tom
Good use of the magnetic lights for testing. :thumbup:

I carry a set with me always. I figure it can keep me on the road when moving my boat. It's not ideal without the side marker lights, but better than troubleshooting on a rainy night.

I would not trust the magnets alone. I use a bit of electrical tape to supplement.
http://www.harborfreight.com/12-volt-magnetic-towing-light-kit-69626-8847.html

vic
 
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NBB

Well-known member
Re: Trailer Light Frustration

I found the net to be full of dumb ideas and theories about this problem. Thought I would post the fix here, under a few searchable threads, to solve the issue for fellow Sprinter owners.

Go buy this thing for < $15, I got mine from etrailer.com.

It adds a load resistor so the factory trailer module, when checking for a bulb out, doesn't freak out. Otherwise it freaks out. It's been designed to fix exactly this problem.

You're welcome.

My LED trailer lights would stay on after the key was out, blink fast or not work at all under various conditions and scenarios. Stupidest redundancy programming ever on the part of the manufacturer - didn't even generate a warning light or code. This thing fixes it all.

IMG_1501.JPG
 

wtm1038

New member
Re: Trailer Light Frustration

I have a similar sounding issue with my new boat trailer being towed by my new Sprinter Winnebago View. The LED lights faintly flash on and off at about one second intervals when all systems were off and the key removed. I was told that the e-trailer item 20142 adapter would solve the problem (7 flat pin to 7 flat pin). So I bought one and found that it didn't change the flashing. I am very puzzled about the problem. Winnebago sez it's a MB issue, but the local MB Service guys don't have a clue! This apparently is a common issue with MB products....why are they not stepping forward with the appropriate fix? Any other ideas out there?
 

autostaretx

Erratic Member
Re: Trailer Light Frustration

What you are probably seeing is the Sprinter applying a test pulse of current to the trailer pins (looking for light bulbs).

If it sees a (normal bulb) load, it then tells the anti-lock, ParkTronix and ESP system "hey! we're towing!"

LEDs draw so little power that the "test pulse" causes them to illuminate.

I would not consider this a "problem" that MB should "fix" (other than come up with something that works with J-random manufacturers' idea of a proper LED load). At worst, i'd call it an "undocumented feature" (auto-sensing of trailer and continuous test of bulb condition).
Would you be satisfied if the owner's manual specified "use incandescent trailer bulbs"?

It may even prevent damage to the Sprinter's bulb drivers (avoiding fuse-blows) when your boat trailer is backed into salt water shorting out the tail lights.

Upon re-reading the question (i.e. happens with power off) ... do you have an MB-installed alarm system or immobilizer?
Does it stop blinking if you wait a full two minutes?

--dick
 
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If the trailer has led & the van, standard lights there should be enough resisitence to allow them to function. You might try I dedicated ground to each light, not just a pigtail & screw to the frame, used dielectric grease on each connection too . On the last trailer I wired , there was a ground wire from the plug to all the lights , seems over kill but might be a fix. Please let us what happens .
 

autostaretx

Erratic Member
If the trailer has led & the van, standard lights there should be enough resisitence to allow them to function. You might try I dedicated ground to each light, not just a pigtail & screw to the frame, used dielectric grease on each connection too . On the last trailer I wired , there was a ground wire from the plug to all the lights , seems over kill but might be a fix. Please let us what happens .
If your NCV3 has the MB trailer module/hookup installed, it's a separate computer module that forms its own signals and drivers for the trailer lights. It doesn't care what the Sprinter's bulbs are doing.



--dick
 
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If your NCV3 has the MB trailer module/hookup installed, it's a separate computer module that forms its own signals and drivers for the trailer lights. It doesn't care what the Sprinter's bulbs are doing.



--dick
It's also likely the control unit can be programmed stop looking for bulbs. If reprogrammed to ignore burnt out bulbs it might let the circuit energize properly. Reason I mention such is that I reprogrammed mine when installing a new rear bumper (Odin) and I needed to relocate the license plate. I used an LED license plate bulb fixture and tapped into the trailer harness wiring to energize. I use an Autel Elite scanner that allowed me to turn off rear trailer bulb monitoring, I'm sure MB Star would allow same. Just a thought...
 

pbansen

Active member
Anyone know what value resistor would need to be added to approximate the value of an incandescent bulb? Doesn't seem like much would be required.
 

borabora

Well-known member
Anyone know what value resistor would need to be added to approximate the value of an incandescent bulb? Doesn't seem like much would be required.
The answer depends on the wattage of the bulb

voltage = current x resistance
wattage = current x voltage

If you have a 20 watt incandescent bulb then 20w = current x 12v
20w/12v = current
current = about 1.66 amp

12v = 1.66a x resistance
resistance = 12/1.66 = about 7.2 ohm

But the load resistor will be parallel with the new LED so you can make the resistor a little larger to draw less current.
The actual voltage will be higher but I think the wattage ratings are at 12V
 

mikeme

2015 LTV IB: 2015 3500 V6
Anyone know what value resistor would need to be added to approximate the value of an incandescent bulb? Doesn't seem like much would be required.
100 ohms will do the trick.

You do not need to match the bulb, you need to satisfy the computer checks.

 

autostaretx

Erratic Member
It would be really nice if a 100 ohms resistor works ... that would allow it to only be a 2 watt rating, which is a LOT small than the 25 watt flavor.

W = V^2/R = 14*14/100= 1.96 watts (although i'd probably use a 5 watt rating ...it will handle the heat better)
--dick
 

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