Unknown electrical connector (Thor Siesta)

jmf27614

New member
I have two of these in the rear area under the frame of my Sprinter based RV. They seem to be factory installed. There is a small black box near and inline with each connector. The plug has a clip, so I think it is meant for some permanent use. Any idea what they are for, all my rear lighting and trailer connector works as it should.1B30C26E-6126-44D9-9CBB-59944EB60F0F.jpeg
 

autostaretx

Erratic Member
... and brand of RV , if it's a commercial conversion...

*and* the wire colors (i can't quite make out the middle wire's color(s))

--dick
 

sailquik

Well-known member
Guys,
Since there is "a small black box near and inline with each connector" we might take a guess
that these connectors are for some additional lights, and that there are reverse current diodes
in the "small black boxes".
The diodes are there to convert the single bulb Euro/MB taillights/stop lights to USA specification
dual filament bulbs.
The "trailer wiring harness" for T1N's always included a diode block to convert the Euro single
bulb system to something that would power a dual filament bulb system used in USA specification
trailer tail/brake lights.
Remember the "tales" of poorly installed trailer tow wiring harnesses where the diode blocks were
down in the right rear quarter panel and were often soaked in water that collected in the quarter
panels because the weep holes were plugged up with mud/debris?
Roger
 

jmf27614

New member
T
... and brand of RV , if it's a commercial conversion...

*and* the wire colors (i can't quite make out the middle wire's color(s))

--dick
It is a 2019 Thor Siesta RV, on a 2017 Sprinter 3500. The center is a black wire (white, black, red). It is a weatherproof connector, the yellow portion is a soft gasket.
 

sailquik

Well-known member
jmf27614,
Do you have a multi-meter?
Set if for >12 VDC and then have someone cycle through the tail lights and turn signals.
You should be able to quickly determine if the connectors are powered by the vehicle rear
lights system.
Probably put the red probe on the red wire and the black probe on the black wire.
No idea what the white wire does.
Roger
 

Cheyenne

UK 2004 T1N 313CDi
What are they zip tied to? MB parts or Thor parts?

And where do the wires come from? The convoluted tubing doesn't look MB to me?

Keith.
 

jmf27614

New member
What are they zip tied to? MB parts or Thor parts?

And where do the wires come from? The convoluted tubing doesn't look MB to me?

Keith.
They were zip tied by me to a plumbing drain pipe, Thor left them hanging. I have no idea of the origination of the wires since that tubing feeds into a larger Wiring bundle. Thor has no other connectors like that.
 

jmf27614

New member
Guys,
Since there is "a small black box near and inline with each connector" we might take a guess
that these connectors are for some additional lights, and that there are reverse current diodes
in the "small black boxes".
The diodes are there to convert the single bulb Euro/MB taillights/stop lights to USA specification
dual filament bulbs.
The "trailer wiring harness" for T1N's always included a diode block to convert the Euro single
bulb system to something that would power a dual filament bulb system used in USA specification
trailer tail/brake lights.
Remember the "tales" of poorly installed trailer tow wiring harnesses where the diode blocks were
down in the right rear quarter panel and were often soaked in water that collected in the quarter
panels because the weep holes were plugged up with mud/debris?
Roger
Another guy thought the black boxes were some sort of ballast because the RV tail lights are LED and MB has incandescent ones, that doesn’t seem right since the connector is wired directly to the small black box Without a split between. I asked Thor Tech support and they couldn’t provide an answer.
 

autostaretx

Erratic Member
MB uses two-color wires for their tail light circuits (except plain Brown for "ground").
Example (2007 diagram):

TailLightLeft.png

As you can see, there is that suspicious little item on the lower right ... but its feed wire is Black with a White stripe.
(the Right turn signal wire is the same color).
The trailer circuits are also dual-color wires.

--dick
 

Aqua Puttana

Poly - Thread Finder
T

It is a 2019 Thor Siesta RV, on a 2017 Sprinter 3500. The center is a black wire (white, black, red). It is a weatherproof connector, the yellow portion is a soft gasket.
I would just assume that it is not MB Sprinter OEM and call Thor to ask them for information. If it is trailer wiring related I would ask for details on the matching connector/assembly information. Even if you don't anticipate using the connectors, it may be good to get the parts in hand before they become difficult to source, or worse go out of production.

Alternatively, is there a Thor forum? It may be a common part for other models.

:2cents: vic
 

jmf27614

New member
I would just assume that it is not MB Sprinter OEM and call Thor to ask them for information. If it is trailer wiring related I would ask for details on the matching connector/assembly information. Even if you don't anticipate using the connectors, it may be good to get the parts in hand before they become difficult to source, or worse go out of production.

Alternatively, is there a Thor forum? It may be a common part for other models.

:2cents: vic
Thor tech support couldn’t answer and I got only guesses on the Thor forum so far. Nothing definitive. I have a working trailer hitch connector. It just bugs me I have plug connectors with an unknown purpose with some module attached. I will have to investigate when I have a chance with a multimeter.
 

Aqua Puttana

Poly - Thread Finder
... Nothing definitive. I have a working trailer hitch connector. It just bugs me I have plug connectors with an unknown purpose with some module attached.
...
Seems odd. I hear you. Was there any brand name on the modules? Maybe for ground effect lighting that was removed?

Not that you asked...
I'd smear some Vaseline or silicone grease over the open ends of the connectors to help exclude moisture and reduce corrosion.

vic

Added:
I moved the thread to Conversions Talk with the idea that those modules and connectors may be used on other brands, not just Thor. FWIW. The thread will get less views and likely less play here in the Thor section. (The Thor people that were questioned so far had no information.)
 
Last edited:

Hooligan2

Member
My 2016 Siesta Sprinter also has the "boxes" I originally thought they were converters but RV dealer said they are load for LED tail lights. (There is a box on both sides near the hitch). Neither has anything connected to the pigtail.DSCF1275.JPG
 

autostaretx

Erratic Member
"Load" for the LEDs ... so the boxes probably contain a resistor (or two) ... needed to make the Sprinter think there's a "real" bulb out there
(they could also be relays: the normal light power pulls in the relay (and it would "click" if blinking) and the relay contacts route power (from a separate circuit) to the unknown (future trailer?) bulbs

If it was "just a resistor", it would be dumping about 20 watts if for brake and directionals, 5 watts for tail lights.

--dick
 

Hooligan2

Member
They are Lightech 019-10-042 load resistor. Early wiring diagram from dealer. Tail Light2.jpg
 

autostaretx

Erratic Member
(almost) Hidden in the upper left corner of that drawing is that all of the resistors are 10 ohms.
So each resistor is dumping 14 to 20 watts (W = V*V/R)
There are only two resistors, one for each directional signal.

--dick
 

Top Bottom