2020 Navion Backup Light Issue

[eyecando]

I'm having an issue with the passenger side backup lamp on my 2020 Navion. When I put the vehicle in reverse, the passenger side lamp will flash on for about 1/4 of a second before turning off. It will do this at least twice. The driver side backup lamp works as expected.

I removed the passenger side backup lamp and verified the same situation occurs with lamp disconnected by using a voltmeter to monitor the signal with the wiring to the lamp open circuited.

I attached the only drawing I have been able to find. Unfortunately, it is of limited use and does not show the actual wiring, only the routing of the factory wiring that connects to the chassis wiring.

I would have expected to have one output from the chassis that supplies both backup lamps, but I can't tell if that is the case.

Has anyone else experienced an issue like this or have any ideas on how to resolve it? It may be an issue with the chassis, but the Mercedes dealer will not look at it.

[eyecando]

With the right (passenger side) backup lamp disconnected, I read 10.8 ohms between the two terminals.

With the left (driver side) backup lamp disconnected, I read 204k ohms between the two terminals.

The right lamp positive is a brown wire on at the lamp end connected to a red wire on the harness end. This red wire connects to a yellow wire with a marking of 329299-01-000(G) 1-TR2.

The 4 pin connector described in note 1 on the drawing I attached on my last post actually has 5 pins and 5 wires.

Unplugging both the 5 pin and the 6 pin connector removes the ground on the white wire. Each of the two connectors supplies the ground connection to both lamps.
With both the 5 and the 6 pin connector disconnected, I read 10.8 ohms between the positive wire and chassis ground on the right lamp. The white wire is floating at this point. Both connections on the left lamp read infinite ohms to chassis ground.

I’m trying to figure out where the 10.8 ohm reading is coming from. Obviously, something in the chassis is wired incorrectly.

With both the 5 and 6 pin connectors disconnected, I used a portable 12 volt source to backfeed the right backup lamp and all 5 of the upper rear clearance lights all lit up! Obviously, something is not right here, but I have never had an issue with the clearance lamps. They work as designed.

It appears that the right backup lamp is connected somehow with the upper 5 clearance lamps, but the right backup lamp doesn’t illuminate when the upper clearance lights are on with normal connections.

I suspect the 10.8 ohm reading is somehow related to one of the three 10 ohm resistors under the passenger seat. I haven’t seen any wiring diagrams to indicate what the resistors are used for, but I would assume they parallel the left, right and tail lamp circuits to make the LED lamps simulate a real bulb.

[Morich]

OUCH! You have flat walked into a big guessing game, where you really need more wire by wire info that we don't get, so we have to start guessing.
Myaybe we can start with a few points that we can be pretty sure of and build from there?

Your wire TR1 is not on the list but I find the number usually means it is one of several for TR. I think you have it right that it is the back up circuit to the lamps.

I looks like the wire assembly ends at the driver side high mount brake lamp, goes up and across the top and down the passenger side, picking up the various lamps on the way before going across the bottom to the driver's side tail, etc.
If that is what you see, do you spot where it connects to the main harness to the front?

Is it this little bit of nothing they show us?


That's pretty close to no help!

But if we go to this drawing and sheet 7 we get the ID that I think you have found :
https://www.winnebago.com/Files/File.../000164549.pdf


The big problem with solid state stuff like this is we have no idea of what the black boxes that things connect to will have in them.
But as a way to look for something odd, what would it show if you look at the resistance of these resisters and especially the top one to see if it is open or something way off from ten ohms?
MS shows as ground for all those, so does a bad resister open or totally shorted only make only one fail ?
That seems stretching quite a bit....
Ten ohms is cutting the specs pretty sharp for a lot of things and they need to be good quality to do it if they are that low?

Maybe a close look for something shorting to ground where that resister is mounted? Loose wire, bent mounting of some sort?

Not a lot of help there but maybe just a different look?

[eyecando]

Unfortunately, I don't think I can get to any of the wiring that goes up the right side and across the top.

I traced the TR2 wire to the backup lamp on the right side. I believe the backup lamp on the left side was labeled TR1.

I'll have to remove the passenger seat to get to the resistors, but I will check them. I suspect the resistors are 10 ohm + or - 10% and then there is some resistance in the wiring so that has to be what I am reading.

The 10.8 ohm reading may be normal, but what I can't understand is why do the clearance lamps light up when I backfeed the backup lamp circuit with the circuits unplugged from the chassis, but when connected normally with the headlamps and clearance lamps illuminated, why doesn't the backup lamp light up also? I need to think about what could cause this behavior. Seems like there must be a diode or a solid state device in the circuit. Maybe when I backfeed the circuit the current is going through an LED lamp backwards?? But everything but the one backup lamp works as expected in use.

Mike

[Morich]

I'm hoping that you can test and avoid going into the wiring across the top, etc. That's assuming and dangerous but the wire seems like the least likely to be the problem??

I have no proof and never see it explained but looking at lots of drawings, it seems the ID like TR1/TR2 and maybe a TR3 are meant to tell us it is a multi-legged/branched wire with several ends. Maybe TR1 at one light, TR2 at the other and maybe TR at the resister would sound right, except that last drawing above also shows TR1 at that resister, so still have something to figure out on that part.

And that is true for me and LED as I have not had enoguh trouble and no training on them other than just switching out light bulbs at the house and some installing to replace in the RV, so that leaves me in the dark.

I was thinking what I might do and if there seems nothing wrong at the resister, I might think about this way to go.
One is the question of them being soldered in. Is that a problem to remove the joint and resolder?
If you can get them out without lots of trouble, maybe a switch of a resister for another if the testing still leaves them looking good? Sounds like a lot of fuss to swap out resisters if you can just get one loose and test. At least they are not a high tech black box that we can't know what inside!

I don't know if this fits or not. Rather than remove the seat, can you possibly reach under, test resistance from the back to the resister by putting a jumper clip to ground on the near side of the rester and then compare resistance to the jumper on the other end of the resister? Idea being rsitance to ground on first side and then resistance to ground on second side being ten ohms more says the resister is actually ten ohms or close. Any sense to that?

But then moving beyond the resister, I might look at pulling both led bulbs out at the back so that I'm guessing it would then leave just wire from front to back with a branch going to the second bulb. Chjeck that guess before trusting!!!
But if true, I would want to look at the wire for having no voltage under any condition like the other lights on, etc. . Just looking for wire with not crosses to other wires?
If finding none, then maybe a helper to let you look for good connection from front to back by them putting a jumper to ground as you read it.

Sorting out what we mightguess is there?
Resisters? IF they look good and no stray contact like loose wire ends,etc. and they resister measures good? We kind of HAVE to call them good.
Wire to the back? If you have it open at the bulbs and see no voltage and see them good continuity, we call the wire good?

New thought? How about the ground at each bulb in back? We think battery is getting there because it lights for a short time, but ground can be funny and do weird things, so maybe a good time to check it at both bulbs?

I don't think of LED (diodes?) as passing current the wrong way. They are definitely polarity sensitive. That's been my major experience as I can put way more than half of them of those little wedge types in backwards, without even trying!

If all that checks, I'm getting low on ideas! Four days to find the problem and two minutes to fix it!

[eyecando]

The wiring for the lights in the back come through two plugs supplied by the Sprinter chassis. I verified that both plugs supply the ground to the LED 2 prong plugs at the backup lamps. Either plug supplies the ground for both backup lamps. The left positive lamp wire was labeled TR and the right one was TR2. I verified the ground was good at both lamps.

When I tested the circuit by backfeeding the circuit with 12 volts dc yesterday, I had both plugs going to the chassis unplugged. I also had the right side LED unplugged at the lamp.

I got to thinking that maybe all my testing had not actually indicated a problem. Maybe the clearance lamps that illuminated during my backfeed test were just due to an unknown sneak circuit. So I decided to temporarily jumper the positive of the two lamps together through a 3 amp fuse. When I did this, the left backup lamp went out immediately and the right lamp did not come on. This told me the circuit was not capable of handling the 10 ohm load since the fuse did not blow. I verified the left lamp started working again after I shut the vehicle down and started it back up.

I removed the passenger side seat and unplugged the 10 ohm resistor that had the TR wire label. I actually unplugged the grounded side. I tested the resistor and it read 10.2 ohms and the 10.8 ohm reading at the right backup lamp went up to 204k ohms.

Tested the lights and everything works normally now! Problem solved.

I suspect the resistors were needed for an older model Sprinter that used bulbs but maybe mine was designed for LED bulbs. So, I believe this was a Winnebago design error.

This has got me wondering if the other 2 resistors are needed. My turn signal indicators inside the vehicle blink faster than they should. I suspect this might also be due to a resistor Winnebago added to the circuit. That's a job for another day.

[Morich]

I think I follow what you are saying but not so sure I would bet much! So since it seems okay, maybe just some added thoughts to compare?

About my only work with LED and even close to design has been in building LED light fixtures for over fish tanks. In that use we often used a resister to limit the current flow thorugh the LED. We would string several along a path and use the resister to limit current if one of the LED failed. When first starting, many would line up enough LED to use the full amount of current coming out of the power supply, but then when one failed, it started a chain and blew the rest of the string. We might be using 15-20 LED in a row, so protection was important.

I'm trying to relate that to what you are finding on these LED. Does it sound right that they wired two LED in parallel and then added the resister to keep the current from going too high if one or the other failed?

That's going pretty far out and memory is not really clear on the whole idea, so if it doesn't ring any bells with you, I'm okay with that!

While here and thinking about LED bulbs, the name "canbus" came to mind and it is something newer than I have looked at but tends to come on EU cars that let us know when a bulb has failed. Mercedes comes up.
Do you have any warning on the dash that a light may be out? That seems to be what I'm finding on a quick search!
Controlled Area Network bus is CANbus???? A small computer network which tells us when a light bulb is out somewhere?

https://www.autobulbsdirect.co.uk/bl...ix-with-video/

If you have it working, I'm good with that and may not need to learn more but is it possible the RV has some bits of design which is not common to US design?
Several things on my cars are beginning to run way out of my "learning curve"!!!

[eyecando]

Richard

I have no alarm or error messages on my dash.

As you indicated, resistors are sometimes placed in series with LEDs to either lower the voltage supplied to the LED or to prevent the failure of one LED from taking down other LEDS or devices due to the excessive current due to a shorted LED.

If the vehicle is designed for bulbs, then CANBUS would probably be set to detect a current below about 1 amp. If it was designed for LEDs, the CANBUS would be set to detect a much lower current in the milliamp range.

In this case, the resistors were placed in parallel with the LED to fake out the CANBUS system. Normally the system would detect a bulb filament opening by monitoring the decrease in current. Bulbs usually draw currents measured in amps while LEDs draw currents measured in milliamps.

A vehicle manufacturer would never place resistors in parallel with LEDs if the system was designed for LEDs. That would have the effect of disabling the dash alarm.

People who run into issues with dash messages is caused by installing LEDs in a vehicle designed with bulbs. In that case resistors are placed in parallel with the bulb to eliminate the dash message caused by low current.

Vehicle manufacturers also include dash alarms to indicate currents above normal in some cases.

Since Winnebago thought the system was designed for bulbs, they added resistors in parallel to increase the LED current above the setpoint of the dash alarm. The disadvantage of this system is that they faked out the CANBUS system and it would never alarm for an open bulb since the circuit would still be sinking 13.6v/10 ohms or about 1.36 amps not including the LED itself. This would be well above the low current setpoint used to detect an open bulb.

Another indication that this was a design error is that separate circuits were provided by the Sprinter for each of the 2 backup lamp circuit, but the parallel resistor was only placed across one of the lamp circuits.

I don't know for a fact that my 2019 Sprinter chassis was designed for LEDs but that's what the indications are. I'll know more when I get around to disconnecting the other 2 resistors and see if that causes any issues. There's always the possibility that the LEDs Winnebago installed draw much less current than the design of a Sprinter LED, but I doubt it.

Thanks for your help in providing diagrams and comments that jolted me into thinking about what the problem could be and resolving the issue.

Mike

[Morich]

When it comes to the Canbus issues, I'm sure about all I would do is ask questions, so if it helps, we'll call it good!
I'm finding far more things that no longer interest me enough to study them too much.
Family issues with one son who has had covid issues since Jan 2020 is now one of my main issues to study and wonder. It seems like the med folks are still just guessing there also!
It seems there is no real answer for what to do, so thinking about electrical issues is kind of my safe haven where at least I can guess at some answers!