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Old 02-13-2019, 04:06 PM   #1
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All Tail lights come on when shifting to Reverse

2016 MBS 2401R. Anyone know why all tail lights would come on when selecting reverse? Just started happening. Also when turning head lamps or parking lights on the Backup white lights come on. Anyone have access or know where to go to get wiring diagrams for the FR Chassis part or the MBS connectors to the rear cabin area? MB blames, FR and FR says its MB. At a tug of war loss. I need wiring for tail lamp assy. It's not the Curt controller.
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Old 02-13-2019, 04:22 PM   #2
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Wiring diagrams for 2401R Tail lights

Anyone help on wiring diagram for 2016 MBS Forester 2401R wiring diagrams for the tail light assy and backup lights. MB and FR finger pointing. I have AC and DC cabin wiring diagrams but nothing for exterior lighting.
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Old 02-13-2019, 04:53 PM   #3
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I would take apart the 7 way outlet and look for stray wires or corrosion.
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Old 02-13-2019, 05:12 PM   #4
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I would take apart the 7 way outlet and look for stray wires or corrosion.
How would that help track down tail light issues in a motor home
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Old 02-13-2019, 05:16 PM   #5
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How would that help track down tail light issues in a motor home

My motorhome has a 7 way outlet at the rear. I have seen where a single strand from one wire, lets say reverse, is now touching the tail light wire. Put the shifter in reverse and now you have reverse lights and tail lights. Bad grounds do some crazy stuff also.
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Old 02-13-2019, 05:17 PM   #6
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My motorhome has a 7 way outlet at the rear. I have seen where a single strand from one wire, lets say reverse, is now touching the tail light wire. Put the shifter in reverse and now you have reverse lights and tail lights. Bad grounds do some crazy stuff also.
OK, got it. Just asking.
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Old 02-13-2019, 05:46 PM   #7
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I would take apart the 7 way outlet and look for stray wires or corrosion.
Yes sir took the entire assy apart no shorts and no frayed wires or corrosion, Thanks
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Old 02-13-2019, 05:47 PM   #8
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Also, try pulling the bulbs out of reverse socket and see if it still lights up tail lights. Seen crazy bulb stuff too
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Old 02-13-2019, 06:29 PM   #9
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There have been all kinds of issues with the taillights. It's important to note that the setup on these Sprinter motorhomes is pretty much different from any other vehicle. In particular, the taillights (and marker lights and backup lights and brake lights) are not driven directly by the Sprinter chassis. FR has installed a taillight control interface between the chassis and all those lights and the trailer plug lights as well. That's why a problem in the 7 way can be reflected all over the place.

Anyway, there have been problems with the controller module such that it was subject to recall a few years ago...and folks have still had problems with the newer controller. So it might be related to the controller. Or it might not. But, after the 7-way, that's probably where I'd start to look.

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Old 02-13-2019, 10:23 PM   #10
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There have been all kinds of issues with the taillights. It's important to note that the setup on these Sprinter motorhomes is pretty much different from any other vehicle. In particular, the taillights (and marker lights and backup lights and brake lights) are not driven directly by the Sprinter chassis. FR has installed a taillight control interface between the chassis and all those lights and the trailer plug lights as well. That's why a problem in the 7 way can be reflected all over the place.

Anyway, there have been problems with the controller module such that it was subject to recall a few years ago...and folks have still had problems with the newer controller. So it might be related to the controller. Or it might not. But, after the 7-way, that's probably where I'd start to look.

Dave


Thx, I have replaced the controller and same issue. I’m a 20 AE/AT aircraft electrician. I’m taking it to Mercedes dealer for them to check the chassis wiring and I’ll go from there.
Appreciate the help.
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Old 02-14-2019, 03:57 PM   #11
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Crazy bulb stuff

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Also, try pulling the bulbs out of reverse socket and see if it still lights up tail lights. Seen crazy bulb stuff too
The "crazy bulb stuff" happens when a dual-filament lamp fails such that one filament breaks and drops down, shorting to the other. Then, for example, a left turn signal could cause all four parking lights to flash, or braking could cause the bright filament of both front lights to light.

The OP's problem includes backup lights. Since backup lights are single-filament lamps, they would not be subject to this failure mode.

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Old 02-14-2019, 05:07 PM   #12
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Thx, I have replaced the controller and same issue. I’m a 20 AE/AT aircraft electrician. I’m taking it to Mercedes dealer for them to check the chassis wiring and I’ll go from there.
Appreciate the help.
I too was an AT on F-4/F-14/F-18 Aircraft for 24 years so I know it is not something easy if you can't find it. It gets more complicated because the RV Builder taps into the Sprinter wiring and does not provide any diagrams of what they did. I figured out a lot of it myself and fixed numerous chafing wires with heat-shrink, spiral wrap, teflon tape and just a lot of tie-straps.

First time I looked under the MH I saw the the Curt Trailer Junction Box just hanging by the wiring, I thought this is a problem waiting to happen. I cleaned all the wiring up, sealed it, put it in a water proof bag and tied it to the frame. No problems in several years.

Anyone owning a Motorhome should crawl under ever inch of it and look for potential chafing and water intrusion problems and tie it up real good.
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Old 02-14-2019, 06:30 PM   #13
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First time I looked under the MH I saw the the Curt Trailer Junction Box just hanging by the wiring, I thought this is a problem waiting to happen. I cleaned all the wiring up, sealed it, put it in a water proof bag and tied it to the frame. No problems in several years.

After the recall was addressed on my rig I had strange issues with the lights as well. Unplugged the junction box connecter, dried it out and put it back together, sealed it and voila, no more issues.
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Old 02-14-2019, 06:39 PM   #14
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They tail lights are a modular type with LED assy’s.
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Old 02-14-2019, 06:40 PM   #15
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I too was an AT on F-4/F-14/F-18 Aircraft for 24 years so I know it is not something easy if you can't find it. It gets more complicated because the RV Builder taps into the Sprinter wiring and does not provide any diagrams of what they did. I figured out a lot of it myself and fixed numerous chafing wires with heat-shrink, spiral wrap, teflon tape and just a lot of tie-straps.



First time I looked under the MH I saw the the Curt Trailer Junction Box just hanging by the wiring, I thought this is a problem waiting to happen. I cleaned all the wiring up, sealed it, put it in a water proof bag and tied it to the frame. No problems in several years.



Anyone owning a Motorhome should crawl under ever inch of it and look for potential chafing and water intrusion problems and tie it up real good.


Yep, after Mercedes confirms it’s not forward of the disconnect, that’s what I’m going to do! Crawl and document! Thx.
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Old 02-14-2019, 07:06 PM   #16
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Agreed Larry. We probably have seen bulbs crammed into incorrect sockets too from factory. But as another pointed out, sounds like they are led panels.

Hell, I’ve seen a dual bulb shoved into a single socket and damn thing set a check engine light for a trans shift issue. Bad thing is Honda was aware of this problem.
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Old 02-14-2019, 07:42 PM   #17
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Here is a link to a mod I did to protect the Curt taillight controller. The recall by FR replaced the Curt with a Hopkins and added an inline fuse, but based on reports on this forum, the Hopkins controller fails too. Unfortunately, the recall does not address the issue that some of us think is the root cause - mounting the controller outside of the vehicle on the rear bumper in line with tire spray.
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