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06-15-2019, 08:42 AM
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#1
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3 Rivet Member
2013 Interstate Coach
Idaho Falls
, Idaho
Join Date: Jul 2017
Posts: 118
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Trailer plug wiring problem
We are getting ready to tow a toad behind our IS. As a first step I wanted to make sure the plug on the IS was wired correctly. Using a volt meter I found that every terminal except for the ground terminal on the 7 pin receptacle is hot all the time even with the key off. The only one that is supposed to be hot all the time is the charge terminal.
I can see where maybe the charge wire may have worn thru to another wire but not all of them.
We bought the IS used and I am pretty sure the previous owner towed a golf cart so I am surprised to have this problem.
The MB dealer is 3 hours away so I am hoping not to have to go that route.
Ant thoughts?
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06-15-2019, 08:53 AM
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#2
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Rivet Master
1972 31' Sovereign
1975 31' Excella 500
Currently Looking...
Benton
, Arkansas
Join Date: Mar 2013
Posts: 5,868
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That's an unusual situation, but my approach would start by taking the plug apart and working backwards.
If I thought the problem went all of the way back to the crazy Chrysler/Mercedes "buss" well...
__________________
The fact that I am opinionated does not presuppose that I am wrong......
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06-15-2019, 09:15 AM
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#3
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3 Rivet Member
2013 Interstate Coach
Idaho Falls
, Idaho
Join Date: Jul 2017
Posts: 118
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I did separate the receptacle by pulling the plug out of the back of it. I then tested the plug with the same results. The next step would be to pull the wires out of the plug and test the individual wires but I do not see how to do that without cutting the wires.
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06-15-2019, 09:50 AM
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#4
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3 Rivet Member
2013 Interstate Coach
Idaho Falls
, Idaho
Join Date: Jul 2017
Posts: 118
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Since MB has its own way of doing things is it possible that it is supposed to have voltage to each terminal and then it is managed by a controller somehow? Seems unlikely but has anyone else checked the voltage on their MB receptacle?
I know my Ram and GMC do not have constant power except to the charge terminal.
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06-15-2019, 10:50 AM
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#5
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Rivet Master
2007 22' International CCD
Corona
, California
Join Date: Jul 2013
Posts: 9,180
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It may be a ‘phantom’ voltage caused by the electronics in the vehicle. A sensitive multimeter May see a voltage that the trailer may not.
Try using a test light instead to trace wiring in this case. Also, even though it’s MB, the 7 way plug should be dead standard. I’d be more worried about getting the Toad wired right.
__________________
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.
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06-15-2019, 12:16 PM
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#6
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Contributing Member
2018 Interstate Grand Tour Ext
Austin (Hays County)
, Texas
Join Date: Jun 2002
Posts: 7,164
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The connectors are monitored by the Sprinter through the CAN bus. The high voltages you see probably very high impedance.
When I plugged in my transmitter for my wireless tow lights, the turn signals did not work unless I stepped on the brake pedal, as well. The transmitter did not pull enough current to let the Sprinter know it was there. I bought a plug with built-in resistors. Voila! My tow lights work.
For the Sprinter to monitor the connectors, there is probably a high impedance voltage there.
Try it with a trailer hooked up and it will probably work.
__________________
John W. Irwin
2018 Interstate GT, "Sabre-Dog V"
WBCCI #9632
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06-15-2019, 02:34 PM
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#7
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3 Rivet Member
2013 Interstate Coach
Idaho Falls
, Idaho
Join Date: Jul 2017
Posts: 118
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I had been reluctant to plug it in in case there was a cross wire issue. However I went ahead and plugged it in to my boat trailer (the toad is not wired yet - tomorrow’s project). Everything worked.
So it must be something with the MB system that allows some voltage to always be there.
Thank for everyone’s input. I am still going to run it by MB to see if there is an issue. If so I will post it back here.
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06-16-2019, 12:33 PM
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#8
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Rivet Master
2018 Interstate Lounge Ext
LV
, Nevada
Join Date: Feb 2018
Posts: 2,580
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Quote:
Originally Posted by Pahaska
The connectors are monitored by the Sprinter through the CAN bus. The high voltages you see probably very high impedance.
When I plugged in my transmitter for my wireless tow lights, the turn signals did not work unless I stepped on the brake pedal, as well. The transmitter did not pull enough current to let the Sprinter know it was there. I bought a plug with built-in resistors. Voila! My tow lights work.
For the Sprinter to monitor the connectors, there is probably a high impedance voltage there.
Try it with a trailer hooked up and it will probably work.
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PASSINTHRU - I had similar experience a long while back when I was trying to use the 7 Pin connector/plug on my 2018 to test out the very teeny 2nd rear cam with also a very low current draw wireless transmitter as JOHN). The only diff is I remembered my voltmeter measurements were exact opposite of your experience,( i.e. I could not force a good few of them to go hot regardless of where I plugged the low-current wireless cam on); except I think on the terminal that is dedicated to be the (+ Hot). JOHN is right in that a lot of those terminals are monitored by the CANBUS. As soon as I plugged in a load with enough resistance that generated enough of a current draw, those terminals cam alive with their respected triggers (i.e. LF turn, RT turn, Stop, Reverse). Good luck
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06-18-2019, 11:12 AM
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#9
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2 Rivet Member
2014 Interstate Ext. Coach
Las Cruces
, New Mexico
Join Date: Oct 2014
Posts: 29
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Trailer Plug Wiring Problem
During March driving over a high-centered railroad crossing, the OEM Pollak Trailer Wiring Connector, and its bracket were torn off their location on the draw bar, and crushed. Note, that the location of the connector was originally poorly located, and that later AI models relocated the trailer plug well behind the bumper/hitch. This crushing resulted in the hot 12v shorting out, which blew the fuse in the #14 20a position in the fuse array under the driver's side seat, see photo, and also blew out the trailer wiring control unit, see photo, which is mounted in a rack inside the box which supports the driver's seat. Replacing the Pollak connector and the control unit did not restore the trailer wiring. As it is a MB system for US requirements, assistance from MB Sprinter Dealerships was sought in the Phoenix area, but was not immediately available as they had no idea how to go about repairing the issue, but would happy to take the AI in for lengthy diagnosis. As these dealerships are at a distance from us, and as much effort and $$ have been spent already, a MB/Chyrsler trailer wiring kit was purchased from the Sprinter Store for less than $200, and all is well again!
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10-23-2019, 07:01 AM
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#10
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3 Rivet Member
2020 27' Globetrotter
Currently Looking...
Taylor Ridge
, Illinois
Join Date: Sep 2013
Posts: 144
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Quote:
Originally Posted by JJKinnerup
During March driving over a high-centered railroad crossing, the OEM Pollak Trailer Wiring Connector, and its bracket were torn off their location on the draw bar, and crushed. Note, that the location of the connector was originally poorly located, and that later AI models relocated the trailer plug well behind the bumper/hitch. This crushing resulted in the hot 12v shorting out, which blew the fuse in the #14 20a position in the fuse array under the driver's side seat, see photo, and also blew out the trailer wiring control unit, see photo, which is mounted in a rack inside the box which supports the driver's seat. Replacing the Pollak connector and the control unit did not restore the trailer wiring. As it is a MB system for US requirements, assistance from MB Sprinter Dealerships was sought in the Phoenix area, but was not immediately available as they had no idea how to go about repairing the issue, but would happy to take the AI in for lengthy diagnosis. As these dealerships are at a distance from us, and as much effort and $$ have been spent already, a MB/Chyrsler trailer wiring kit was purchased from the Sprinter Store for less than $200, and all is well again!
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How did you access the control unit to replace it? Did you have to remove the driver’s seat?
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10-24-2019, 01:17 PM
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#11
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2 Rivet Member
2014 Interstate Ext. Coach
Las Cruces
, New Mexico
Join Date: Oct 2014
Posts: 29
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The control unit can be accessed underneath the driver's seat, which will be needed moved out of the way by removing the four bolts holding it to the box in which you will find the control unit. Please note that once you have unbolted the seat, you can slide it backwards to allow access to the seat box. I slid the seat on to a box. The seat is not light. Do NOT unplug the seat wiring harness as I understand that the airbag system will need to be re-programmed if the harness is unplugged.
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10-24-2019, 06:37 PM
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#12
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3 Rivet Member
2020 27' Globetrotter
Currently Looking...
Taylor Ridge
, Illinois
Join Date: Sep 2013
Posts: 144
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Great! Thank you for the information!
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