Electrical question

Mike LaB.

New member
I've been reading on this forum that Sprinters (maybe only the T1Ns?) are fussy about adding electrical accessories to the electrical system. The two that come to mind are trailer hitch wiring and horn changes.

I have several accessories that plug into the cigarette lighter/accessory jacks and they don't seem to make a difference. I'm considering "hard wiring" them to eliminate the bulky 12volt plugs. I've also installed a backup camera transmitter to my backup light circuit without any noticable problems being caused.

Can someone explain to me, in laymans terms, what the concerns are with the Sprinter electrical system. If I don't overload a circuit and fuse each addition why would I have any problems?

Another thought. If I install a receiver type tow hitch does the spare tire have to be relocated and what is the most recommended place to relocate it to?

Thanks!
 
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220629

Well-known member
Re: Elactrical question

I've been reading on this forum that Sprinters (maybe only the T1Ns?) are fussy about adding electrical accessories to the electrical system. The two that come to mind are trailer hitch wiring and horn changes.
I can't speak to the horn system except that in adding a larger/louder horn the load on the new unit may be significantly higher.

Trailer wiring can be a problem because the Sprinter computer watches the lighting circuit for things that don't match what it is programmed to expect. If someone just adds lights by putting wires on the existing lamps and extending them out to the new trailer ones the computer sees the bigger loads on that wiring and will see that as a problem. The solutions are to use an OEM harness or a light module on a 12 volt dedicated feeder which draws so little "trigger" power to know when to turn your trailer lights on that the computer doesn't know it is there. A search will get you more details.

I have several accessories that plug into the cigarette lighter/accessory jacks and they don't seem to make a difference. I'm considering "hard wiring" them to eliminate the bulky 12volt plugs. I've also installed a backup camera transmitter to my backup light circuit without any noticeable problems being caused.
To the best of my knowledge you can hard wire your accessories without any problems. I would not advise using the fuse extenders to double up existing fuses because they have been known to cause connection problems in the fuse block.

Can someone explain to me, in laymans terms, what the concerns are with the Sprinter electrical system. If I don't overload a circuit and fuse each addition why would I have any problems?

Another thought. If I install a receiver type tow hitch does the spare tire have to be relocated and what is the most recommended place to relocate it to?

Thanks!
I added a receiver hitch to my 2004 140 2500. There was no major problem with the step bumper (I had to grind the brackets just a wee bit.) and no problem at all with the spare tire. Hope this does some good. AP
 

Mike LaB.

New member
Thanks A P,
That was a big help. I didn't realize that the vehicle monitored current flow (?) in the system. I guess these computerized vehicles have a lot of surprises for someone like me.

So I can leave the spare tire in its place after the hitch installation and if I run a fused power supply from the battery I can put a trailer light hookup in with no problems. Great! Thanks!
 
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220629

Well-known member
Thanks A P,
That was a big help. I didn't realize that the vehicle monitored current flow (?) in the system. I guess these computerized vehicles have a lot of surprises for someone like me.

So I can leave the spare tire in its place after the hitch installation and if I run a fused power supply from the battery I can put a trailer light hookup in with no problems. Great! Thanks!
Mike,
Glad I could help. Not that you asked, but to expand a bit. The OEM harness doesn't just take care of the lights, it also lets the computer know that there is a trailer being towed. That affects the way the computer reacts to a skid situation. Because I tow only about 3000# and towing is relatively infrequent I decided that the installation time and cost was not worth the OEM for my situation. By using a trailer light module as I have one ends up towing without the computer control ESP and ASR aware of the trailer being there. If you plan to tow more weight than I do, or plan to tow a majority of the time I think the OEM harness and included computer control is worth considering. It is a bit pricey and much more involved to install.

If you do go with the module you may want to consider what I installed. When I ran the dedicated 12 volt power back to the left rear of my van I used a larger feed wire. I fused it at 30 amps at the battery (I think...maybe 40. It's a big cable that was already there for a handicap lift) and then split it off to 2ea. fused 20 amp circuits in the area above the rear light pod. One 20 amp went to the trailer module. The other 20 amp went to an accessory (cigar lighter) receptacle for camping use. It has often been convenient to have that 12 power available in the back of the van.

Hope this does some good. AP
 

Mike LaB.

New member
Wow! Again, thanks A P ! I forgot all about the ESP and ASR features. I guess I'll have to chew on this a bit more before I commit to doing anything. I don't have any immediate plans to tow, but I do have a small flatbed trailer and having a vehicle with the capabilities of the Sprinter I just wanted to be able to tow if the need arises.
Now I'm towing with a Ford Focus wagon which is limited to 100 lbs tongue weight and 1000 lbs towing weight. When I retire in about 3-4 years and move a few hundred miles north, having a larger tow load ability will be helpful.
Thanks again for all your insight, it's greatly appreciated.
 
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autostaretx

Erratic Member
Re: Elactrical question

If memory serves, an option for the T1N's (and i think "just there" in the new ones) was a small card with electrical tie-points under the driver's seat, near the rear metal of the pedestal.
It provides (at least) +12v (battery), +12v (switched... only on when the engine is running) and ground.
With the power taps separately fused from the rest of the vehicle.

That might be something to look for.

--dick
 

sikwan

06 Tin Can
Re: Elactrical question

The OEM harness doesn't just take care of the lights, it also lets the computer know that there is a trailer being towed. That affects the way the computer reacts to a skid situation.
How true is this and what was the special wire that the controller hooked up to?

If memory serves, an option for the T1N's (and i think "just there" in the new ones) was a small card with electrical tie-points under the driver's seat, near the rear metal of the pedestal.
It provides (at least) +12v (battery), +12v (switched... only on when the engine is running) and ground.
With the power taps separately fused from the rest of the vehicle.
Mine is mounted on the parking brake side of the metal pedestal. I believe if you see a couple philips head screws on the hand brake side, then it's there.
 

220629

Well-known member
Re: Elactrical question

How true is this and what was the special wire that the controller hooked up to?
sikwan,
Good question. In a thread somewhere/sometime that someone was promoting using the OEM harness and justifying the extra expense/installation cost it was stated that the computer would know the trailer was attached. I believed that because of the way the OEM trailer wiring harness seems to go everywhere but up in routing through the vehicle. Because they connect to specific points in the electrical system it seems reasonable that the computer sees the changes when the trailer is actually connected. If they just wanted to make the lights work it would just need to connect in the rear like an aftermarket module. That said, I defer to one of the big players for clarification as I'm only repeating what I read. Hope this does some good. AP
 

autostaretx

Erratic Member
Re: Elactrical question

From an engineering point of view, the official wiring harness attaches to the -front- of the vehicle to avoid having to make the normal taillight wiring beefy enough to handle unknown amounts of current demands by a theoretical trailer.
By running a dedicated trailer cable directly from the power distribution and fuses, they can "limit the damage" caused by trailer wiring issues (such as backing a trailer taillight into a metal pier post as you're launching your boat).
It's just "better practice".
It also avoids confusing the "one taillight bulb is burned out" -detection logic.

I have no idea if the anti-skid (etc) knows it's there. That (like Cruise Control and fast idle) would seem to be something they'd separately tell the Ecu (and friends) with a DRB-III. I don't remember seeing that step mentioned in the installation notes.

have fun
--dick
 

220629

Well-known member
Re: Elactrical question

From an engineering point of view, the official wiring harness attaches to the -front- of the vehicle to avoid having to make the normal taillight wiring beefy enough to handle unknown amounts of current demands by a theoretical trailer.
By running a dedicated trailer cable directly from the power distribution and fuses, they can "limit the damage" caused by trailer wiring issues (such as backing a trailer taillight into a metal pier post as you're launching your boat).
It's just "better practice".
It also avoids confusing the "one taillight bulb is burned out" -detection logic.
One could argue that a trailer light module using trigger signals has shorter/less wiring so less under vehicle exposure to damage and line loss, less connections to possibly go wrong, built in current limiting and isolation, is easier to install, and is therefore the "better practice" solution. The ECU bad bulb feature hasn't noticed my thieving module trigger signal at all.
I have no idea if the anti-skid (etc) knows it's there. That (like Cruise Control and fast idle) would seem to be something they'd separately tell the Ecu (and friends) with a DRB-III. I don't remember seeing that step mentioned in the installation notes.
have fun
--dick
If it's true that the ECU doesn't know that a trailer is connected using an OEM harness I'm feeling much better about my decision to go with an after market module. That's considering both cost and installation time of the module compared to the write-ups about installing the OEM harness. Thanks for the input. AP
 
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famof8

Famof8 + 1 = Famof9!
So how do we go about figuring out the if the ECU is fed this information? :thinking: With the size trailer I will be towing, it would make a difference.
 

TimJuhl

Member
AP, that is the most succinct explanation of the reasons to use the OEM (or equiv.) trailer wiring harness I have heard. Even I understand now :thumbup:

I have a house battery for most of the auxiliary systems in my van conversion but I did connect my GPS and backup camera to the switched terminal under the driver's seat. Both turn on upon startup. I used inline fuses and have had no problems. If you wish to install something with a significant current draw you may wish to consider running a appropriately sized wire directly to the battery + terminal.

Tim
 

autostaretx

Erratic Member
Well, i dug up the 2002-2006 Trailer Cable installation manual (attached).

MB -does- tap off from the rear light units.
The only wires which run the length of the vehicle are feeds for raw (unfused!) battery power, ground, and the Trailer Brakes line.

(so much for remembering how it was run... but it's been 3 years since i read it...)

have fun
--dick
 

Attachments

220629

Well-known member
famof8,
I thought someone here would have answered this by now. Unfortunately I haven't found anything specific to verify one way or the other.

I searched around here and found that the subject of whether the ECU recognizes that a trailer is connected has been discussed before. (No surprise on that.) Although it was stated by some that it did see a trailer connected, I didn't find anyone really pointing to a source to verify that.

I did a Google search using "mercedes ASR ESP trailer". Using "Sprinter" instead of "Mercedes" didn't get much except forum discussions.

With an OEM harness the Mercedes-Benz Viano does know you stuck a trailer behind it. I can't imagine that it wouldn't be true for the Sprinter also.

Here's the link:

http://www.benzinsider.com/2009/04/mercedes-benz-viano-4matic-winner-in-womens-rally/

Some text:
"Comprehensive safety features

The Electronic Stability Program (ESP), fade-resistant disc brakes all round, anti-lock braking system (ABS), electronic brake force distribution (EBD), acceleration skid control (ASR) and the hydraulic Brake Assist (BAS) are obligatory equip­ment, as are airbags for driver and co-driver. Thorax sidebags (standard equip­ment in the Viano Ambiente) and windowbags are available as optional extras. Adaptive brake lights further enhance the already exemplary safety level.
The Viano is exceptionally safe with a trailer in tow too: trailer stabilisation as an additional function of ESP detects dangerous fishtailing of a trailer or caravan and reduces it by selective braking action. A factory-fitted trailer coupling is prerequisite. ESP trailer stabilisation recognizes a trailer when it is connected to the towing vehicle by means of the electric connector plug during the coupling procedure."

Related info, but not specific to Sprinter either.

http://www.whnet.com/4x4/esp.html

"What is trailer stability assist?
TSA reduces trailer swaying by utilizing ESP sensors and braking systems. It was introduced in 2005.
towing with TSA"

Unrelated, but interesting.
http://www.whnet.com/4x4/sprinter_crashtest.html

If nothing else my post may get others to chime in. Hope this does some good. AP
So how do we go about figuring out the if the ECU is fed this information? :thinking: With the size trailer I will be towing, it would make a difference.
 

famof8

Famof8 + 1 = Famof9!
Thanks AP. It would make sense that the van would know, since it has to adjust for the difference in handling characteristics.

Bret
 

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