Trailer lights

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mholroyd

New member
Help! We have a 2011 Passenger 2500 with factory tow wiring. We have a brand new 12" trailer with LED lighting and brakes.
Everything works, except the left turn signal. It has previously worked on another trailer with incandescent bulbs, but now it's not. A trailer tech went through the system and figures it is the Trailer Control Module. Does that make sense? Alternately, I called a dealership and they think it might just be an issue trying to control the LED lighting and that there is a simple converter that can plug between the two. Does anyone know of this converter (if it exists) or do we need to try and replace the Module? Thanks!
 
autostaretx

autostaretx

Erratic Member
The Trailer Module does check for "dead" bulbs by pulsing them with electricity and measuring the current.
Plain LEDs draw too little current, so the Sprinter thinks they're dead (or the wire is broken).
Brake and Turn Signal bulbs draw more current than the normal tail lights, so that is factored into the mix.

The "fix" is to put a resistor in parallel with the affected wires (this takes a total of 3 or 4 resistors: one for each turn signal, one for the brakes, and (in extreme cases) one for the tail lights. A typical bright filament is 21 watts, so a 6 to 10 ohm resistor capable of handling at least 25 watts would suffice.
The "converter" you spoke of probably does that in a 7-pin-to-7-socket lump.

There have been a few threads within the last 6 months by people who have bought the resistors and soldered or "vampire-tapped" them directly into place on the trailer or van wiring itself.

Here's an example of a "resistor kit with vampire taps": https://www.etrailer.com/Accessories-and-Parts/Putco/P230004C-2.html
(i would slightly prefer https://www.etrailer.com/Accessories-and-Parts/Putco/P230004A-2.html, higher wattage resistors)
Each resistor is connected "across" one lamp: so one tap goes onto the (let's say) Left Turn wire, and the other tap is on "ground".
The other resistor would be tapped on the Right Turn wire, with the other end also going to "ground".
(i'm not a big fan of vampire taps, since they can be a spot for corrosion on the wiring ... sealing them with good tape or potting compound isn't a bad idea)
Here's a typical "how to install them" YouTube video (grabbed at random): https://youtu.be/5yKlQQCMbwg

--dick
p.s. the simple test for "Sprinter's module or LEDs?" would be to borrow an incandescent trailer for a 5 minute hook-up test. If the lamps work, you just need the resistors added to your trailer.
If your new trailer has replaceable "bulbs", then swapping in two incandescent bulbs would suffice for the test.
p.p.s. a quick Googling didn't find a 7-pin-to-7-pin resistor module, and that could be because the resistors DO have to dump a lot of heat (20 each is 60 watts total... hot, just like any 60 watt light bulb)
 
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Düsseldorfer

New member
I agree with everything Dick said. But I don't see how the LED issue would cause just one side of your turn signals not to work. If your right turn signals are LEDs and they work, then your left should too.

I tow a car hauler equipped with LED lights, and the Sprinter's never had a problem with it. So I think somewhere you have something that is "no workie."

Before tackling any of Dick's wise suggestions, I would just get out my cheapie Harbor Freight multimeter and spend a little bit of quality time with the 7-pin connector. Make sure the van is sending the right signals before blaming the trailer. And, make sure the LH turn signal circuit on the trailer isn't open.

I've never heard of a twelve-inch trailer before. Bet it tows like a dream! :smirk: (Sorry, couldn't resist.)
 
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autostaretx

autostaretx

Erratic Member
Following along on Düsseldorfer's comments, how does the Left Turn "not work"?

Bulb off? (could be bad wiring)
Bulb steady on? (good wiring, Sprinter not cooperating)
Bulb rapidly flashing (both on the dash, and outside on the trailer)?

In all three cases, what's the *Sprinter's* Left Turn signal doing at the same time?
(it's driven by a different module)

--dick
 
SSTraveler

SSTraveler

2014 LTV Unity Murphy Bed
I had the same thing happen and solved my problem with this adapter, https://www.amazon.com/57003-7-Way-...7003&qid=1553778567&s=gateway&sr=8-1-fkmrnull. This issue is discussed in greater detail on this thread, https://sprinter-source.com/forum/showthread.php?t=62164&highlight=Curt+adapter&page=3. See #25 for my post on Curt adapter. I first tried the similar Tow-Ready version adapter and it did not work for me so I returned it. The Curt 57003 adapter is the one that worked best for me! You can also try adding a resistor across that light circuit, https://www.amazon.com/4Pcs-Aaron-6...7&s=gateway&sprefix=Canbus+res,aps,187&sr=8-5, to address the Canbus issue. You wire it across the ground and power wires for the turn signal/brake lamp.
 
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old-geezer

Member
Our trailer also has LED's and was expecting the same problems but everything works fine. Ran my VIN and this line item is included. Assuming it's a cutaway chassis thing:

JW2 LAMP FAILURE INDICATOR DEACTIVATION
 
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220629

Well-known member
SSTraveler said:
... Maybe there is a difference between the cutaway chassis, which us what I have, versus the van.
Click to expand...
Commercial conversion units don't necessarily use MB tail lights. As you say though, even if MB branded the NAS aka NAFTA 3500 Cab Chassis models may have different configuration OEM vs enclosed vans.

:cheers: vic
 
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