Tow Lights Wiring Question

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Tow Lights Wiring Question

August 24, 2014, 06:42:40 pm

We have a 2011 Kia Sorento LX 4-cyl FWD Auto. We really like this little SUV, and do not wish to replace it, or buy another vehicle at this time. Therefore, we are determined to use the Sorento as our Towd. With that in mind, I am trying to rig up the vehicle for TWO different functions.

First, I want to be able to pull a small trailer (or a tow dolly) behind the Sorento. I have purchased and installed a Curt hitch #13073. I have purchased a Curt trailer light wiring kit #56163, but have not installed it yet. From my reading on the Kia forums, I have concluded that these items will perform their intended function perfectly.

Second, I want to be able to pull the Sorento on a 2-wheel tow dolly behind our motorhome (sadly, this model Sorento cannot be flat towed). Our Foretravel is already wired with a flat 4-pin trailer light connector that should operate the lights on the tow dolly (we don't have the dolly yet - it is headed this way). When it is being pulled on the dolly, I want the Sorento tail lights, brake lights and separate yellow turn signals to function simultaneously with the tow dolly lights and the motorhome lights.

Question: What would be the simplest way to wire the Sorento tail lights, brakes lights and turn signals so it will work BOTH as a tow vehicle AND as a towed vehicle?

Any assistance or ideas you might provide will be much appreciated! Diagrams will probably be required - I am not a EE.

Re: Tow Lights Wiring Question

Reply #1 – August 24, 2014, 09:17:22 pm

Chuck, I used a Tow Daddy:

Tow Daddy Plug-N-Tow Wiring Universal Kit

Cheers

Ted

Re: Tow Lights Wiring Question

Reply #2 – August 24, 2014, 11:09:39 pm

Ted,

Thanks for the suggestion. I just followed your link, and watched the video. I don't think Tow Daddy would work for me. My Sorento does not have a factory trailer wiring harness. Because of this, the Curt trailer wiring kit for my vehicle uses the exact same type of double plug connection (behind the tail light assemblies) as does the Tow Daddy. I suppose I could install both systems on the car, but I would have to pull the tail lights out and swap plugs each time I switched from "Tow Vehicle" to "Towed Vehicle". It may eventually come down to this, but I was hoping for something a little simpler.

I have been reading about the diode based systems. I am wondering if I could install the Curt trailer wiring kit using the double plugs, and also run separate wires to power the lights through diodes. I only need the 3 bulbs on each rear corner (tail light, brake light, and yellow turn signal) to work when in "Towed" mode. I guess I need to do more research - surely somebody has run into this situation before!

EDIT: I just went back and looked again at the link Ted provided. I realize I jumped to a false conclusion when I watched the video. The video covers installation of a "custom" Tow Daddy kit, with specific connectors for that vehicle. Tow Daddy does not make a specific kit for the Kia. The link Ted provided was for a "universal" Tow Daddy kit. When I took the time to read the instructions for the "universal" kit, I saw it required cutting individual wires and splicing the leads from the Tow Daddy module. This means the Tow Daddy module would function much the same as the diode based kits, except it has the single module in place of multiple diodes. This might be a possible solution!

My apologies to Ted for jumping to wrong conclusion and dismissing his suggestion.

Re: Tow Lights Wiring Question

Reply #3 – August 25, 2014, 03:34:43 am

I would probably wire up the dolly so that it plugs into the motormotor (or other vehicle) and works when it's empty. Then I would tap into the dolly wiring to add a 4 or 6 wire plug to the dolly that would plug into the Kia. Then wire the Kia with a 4 or 6 wire plug on the front. Run wires under the Kia to the back and then wire it to the existing bulbs with diodes or relays.

Plugs: Hopkins Endurance 6-Way Trailer Connector Socket - Vehicle End - Ergonomic
Connect Dolly to Kia: Amazon.com: Roadmaster 98146 6-Wire Straight Power Cord Kit: Automotive

Someone here suggested I use relays instead of diodes because of the voltage drop with diodes. I did and it has worked great. Plus relays are cheap (via Amazon) and are easy to wire in because of the sockets w/leads they plug into. Plus if you ever need a spare you can get one at any auto parts place.
Amazon.com: Genssi (10 Pack) 30/40 AMP Relay Harness Spdt 12V Bosch Style

When I did our toad I actually ordered a socket and base of each size (brake/blinker & tail light) on ebay. Then I wired the relays in so they just plugged into the trucks existing wiring without cutting any wires. But that's not necessary.
Heavy Duty 3157 3057 3155 3357 3457 3757 4057 Wiring Harness Sockets Pre Wired |
3156 3157 Male Adapter Wiring Harness for Headlight Tail Lamp Signal Retrofit |

Attached is the info someone shared with me.

This setup will allow the Kia lights to work with your coach and dolly, without altering how the work when not on the dolly.

Edit: If the Kia has separate brake and blinkers that would complicate matters, but it's still doable. Most likely your going to have to have two plugs on the back of the coach. Does it have separate blinkers?

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Re: Tow Lights Wiring Question

Reply #4 – August 25, 2014, 08:33:34 am

Like all of this, my only concern is electrical draw on the turn signal relay

My suggestion to solve this would be LED for tow dolly and Kia

Re: Tow Lights Wiring Question

Reply #5 – August 25, 2014, 08:41:46 am

I have no idea how the Kia is wired but try this; I have had it work on other vehicles.

Install the new trailer wiring on the Kia, the motor home & the tow dolly. Check it all & make sure it works. Try to use the same plug on all units. I like the standard round RV plugs even though you will not use some of the circuits in all applications. Then, try plugging the trailer plug from the motor home into the trailer plug of the Kia. You will need to make up a cable with 2 male plugs to do this. If the appropriate lights work, you can fabricate a more permanent solution. You can install female plug on the dolly and another on the front of the Kia, hard wired to the trailer female on the back of the Kia.

TOM

Re: Tow Lights Wiring Question

Reply #6 – August 25, 2014, 09:16:53 am

Quote from: ScubaGuy – August 25, 2014, 03:34:43 am

Edit: If the Kia has separate brake and blinkers that would complicate matters, but it's still doable. Most likely your going to have to have two plugs on the back of the coach. Does it have separate blinkers?

Thanks for the great post - lots of info - I'm still trying to digest it. To answer your question, yes, the Kia does have separate brake and blinkers. The rear lights are two-piece assemblies - half on the fender and half on the tailgate. The tailgate half can be ignored - it is only a running light and the back-up light. The half on the fender has two bulbs (bulbs, not LEDs) - one red bulb that functions as both "running light" and "brake light", and one yellow "turn signal" bulb.

Re: Tow Lights Wiring Question

Reply #7 – August 25, 2014, 09:24:13 am

Quote from: fouroureye – August 25, 2014, 08:33:34 am

Like all of this, my only concern is electrical draw on the turn signal relay
My suggestion to solve this would be LED for tow dolly and Kia

I share your concern. The tow dolly will have LED lights, so very little added load there. I have checked the turn signal relay on the coach, and it is the more modern electronic "variable load" type. I think it was added by the PO when he installed the trailer light harness. He also provided both type trailer sockets - round and flat. Thanks, John!

Re: Tow Lights Wiring Question

Reply #8 – August 25, 2014, 09:37:21 am

Quote from: OldManSax – August 25, 2014, 08:41:46 am

Then, try plugging the trailer plug from the motor home into the trailer plug of the Kia. You will need to make up a cable with 2 male plugs to do this.

Tom,

Great minds think alike! I was wondering to myself last night what would happen if I connected the two trailer leads. Assuming they both follow the correct "standard" wiring protocol, the circuits should match up. The only problem I can see is that the Curt trailer wiring harness for the Kia uses a "converter box" between the light bulbs and the output plug. I think this is necessary to convert the Kia lights (separate tail light, brake light and turn signal) into a 4-wire flat plug circuit with a single common brake light/tail light wire. I think the "converter box" is probably "one way", similar to a diode, and will not allow the power to pass through the harness backwards.

But what the heck - it's certainly worth a try!

Re: Tow Lights Wiring Question

Reply #9 – August 25, 2014, 10:04:17 am

I appreciate all the good ideas! Somewhere in this thread I am sure is the answer I seek. I just need to figure it out. I think the best idea (thanks Tom) is to get the Curt trailer wiring harness installed on the Kia, and make sure it works. Then get the tow dolly put together (it should be delivered tomorrow) and make sure the lights work when connected to trailer harness on Kia and on motorhome. THEN, figure out how to wire in the additional "towd" function on the Kia.

Will probably be back with more questions at that point - stand by!

Re: Tow Lights Wiring Question

Reply #10 – August 25, 2014, 10:16:59 pm

Chuck,

What about this? If the Curt unit has a converter box, you could wire the FRONT plug on the Kia AHEAD of the convertor box. The harness has already been connected to the Kia rear light at that point.... (maybe!)

I'm just talking through my hat here...... I've never even opened the hood of a Kia! But, I've never let ignorance & stupidity stop me before!

TOM

Re: Tow Lights Wiring Question

Reply #11 – August 26, 2014, 09:03:30 am

Tom,

Once again, I am right with you on the thought process - i.e. splicing into the Curt harness ahead of convertor box. The Curt harness gets 3 "signals" from the driver side light plug adaptor: tail light, brake light, and of course left turn signal. It has a separate wire (with double plug adaptor) that runs across the back to the passenger side light to pick up the right turn signal. The turn signals would be simple - just tap into the appropriate wires upstream of convertor. The brake and tail light connection would require additional jumper wires run across to the passenger side.

I think diodes would still be required, but I have to think about where they would go. Will be easier to visualize once the Curt harness is installed in Kia.

I think this might be the simplest (and cheapest) way to go. A generic 4-pin flat plug with wire is $15. If required, I can get 4 diodes on eBay for $35 . The Tow Daddy might work (instead of diodes), but it's $110 just for the box. ScubaGuy's idea of using relays instead of diodes is interesting, but seems a lot more complicated, and not much cheaper.

Tow dolly should arrive today. I'll get it put together, and get the Kia wired up to pull a trailer, then go from there. Thanks for the "brainstorming"!

Re: Tow Lights Wiring Question

Reply #12 – August 26, 2014, 09:37:23 pm

OK, I'm gonna show my ignorance here....

Why would you need diodes? When the Kia is off & being towed, electricity would go to Kia lights. When Kia is being used, electricity would end at plug .

Anyway, if anything else lights up, it's just extra!

TOM

Re: Tow Lights Wiring Question

Reply #13 – August 26, 2014, 10:38:22 pm

Quote from: OldManSax – August 26, 2014, 09:37:23 pm

Why would you need diodes?

The way I understand it, there is some concern about pushing voltage "backwards" through the vehicle's wiring harness (especially on newer vehicles). I don't know what exactly is supposed to be harmed by this - just that it is to be avoided. There must be some basis for this concern - otherwise why would the diodes even exist? I guess I need to read more on the subject...

Re: Tow Lights Wiring Question

Reply #14 – August 27, 2014, 07:08:41 am

I bought the universal Tow Daddy setup a couple of years ago and noticed at the end of this winter that some things weren't working. The deep snow up north appeared to have ripped some of the wiring out of the harness. I tried to contact Tow Daddy but couldn't get ahold of them and it looks like they may have been bought out by Hopkins, who have made some improvements to the universal harness though without the built in lights.

Amazon.com: Hopkins 55999 Towing Solutions Towed Vehicle Wiring Kit: Automotive

Let me say this, the universal harness works but is far less desirable and simple to install than the custom made options especially for $100+. For $40 though, this unit isn't too bad.

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Re: Tow Lights Wiring Question

Reply #15 – August 27, 2014, 05:40:52 pm

The stock lighting available with a tow dolly is legal without tail light wiring for the towed vehicle.

Re: Tow Lights Wiring Question

Reply #16 – August 27, 2014, 06:10:09 pm

Quote from: Dave Head – August 27, 2014, 05:40:52 pm

The stock lighting available with a tow dolly is legal without tail light wiring for the towed vehicle.

Legal (in all states?), perhaps...I'm not really up on all the state towing laws. Something else to study...

Safe? Not in my opinion. Lots of angles where the Towd will block view of one of the dolly lights, and might even block view of coach lights.

I want my Towd lights working (minimum of 2 red tail lights, brake lights, and turn signals), one way or another. That's just me.

Re: Tow Lights Wiring Question

Reply #17 – August 27, 2014, 11:13:54 pm

There will be a reply from someone who knows more about this subject than me but I will say that I believe if no diode or "check valve" is used the reverse flow of current WILL cause the lights to ultimately burn out. maybe it is something to do with double the voltage going to lights when brakes etc are activated in coach. Someone will explain this better but most probably in 5 pages of script. I did not use diodes at first but after losing lites a few times I put them in and guess what-it works!! Do not argue just do it

JohnH

Re: Tow Lights Wiring Question

Reply #18 – August 27, 2014, 11:28:47 pm

I did a little reading on the subject of lighting requirements for a car in tow on a dolly, when the dolly is equipped with lights. Seems to be a lot of differing opinions. In general, most commercial entities in the towing business (either selling or renting equipment) state that operative lights on the rear of the towed vehicle "are required by law". This position may be due, at least in part, to liability concerns.

In contrast, when the subject comes up on most RV forums, the general consensus seems to be that lights are not legally required, but a lot of people run them anyway just to be safe. Some specific state examples usually pop up, supporting whichever position is held by the forum member.

Here's a couple examples from the "Lights are Required" camp:

The U-Haul "Tow Dolly User Instructions" says, "Even though the tow dolly has operating lights the law requires that a vehicle-in-tow rear-end be equipped with functioning stop, turn and running lights. Detachable vehicle-in-tow towing lights can be purchased at your U-Haul Center or dealer."

RVSafely.com says, "The law also requires that the towed vehicle have operable lights. The lights should be wired to operate from the motor coach and must include brake lights, turn indicators, and running lights while traveling at night. Laws can vary from state to state. For example, in Georgia, if you use a tow dolly and the rear of your vehicle extends four feet beyond the lights on the dolly, you must use some type of lighting on the rear of the towed vehicle itself. You cannot use the dolly's lights to satisfy this requirement. Check with your state to make sure you are staying within its guidelines."

Even if your home state does not require lights on the dolly-towed vehicle, do not assume that this will protect you from legal troubles in every state. It was pointed out on several forums that equipment laws do not fall under reciprocity agreements between states. I.e., to be legal you must comply with the equipment regulations of each state through which you travel. Better safe than sorry!

Re: Tow Lights Wiring Question

Reply #19 – August 27, 2014, 11:42:48 pm

you are correct Chuck unless you stay in one state make it conform to ALL States (and provinces) We in Canada have 1 law for all the country so there is NO guessing. Brakes needed on all tow vehicles, Licence requirements for air brakes in all Provinces. This makes sense so there is no saying "Duh, Officer, I did not know"
John H

Re: Tow Lights Wiring Question

Reply #20 – September 10, 2014, 09:35:24 am

Quote from: ScubaGuy – August 25, 2014, 03:34:43 am

I would probably wire up the dolly so that it plugs into the motorhome (or other vehicle) and works when it's empty. Then I would tap into the dolly wiring to add a 4 or 6 wire plug to the dolly that would plug into the Kia. Then wire the Kia with a 4 or 6 wire plug on the front. Run wires under the Kia to the back and then wire it to the existing bulbs with diodes or relays.

For the 2 or 3 people who might actually remember this discussion thread, and wonder what I finally did, here is the answer. I basically went with ScubaGuy's suggestion, with one slight modification - I decided to totally avoid using diodes and relays. After studying the tail light assembly on my Sorento, I realized there was plenty of room in the red section of the housing for adding a second bulb. I purchased a "bulb and socket" kit, installed it, and it works great. The only hard part is running the wiring under the car where it is protected from damage. (Remember the good old days when cars had separate frames made of "C" channel steel? The perfect place to run accessory wiring) Using this kit, when the Sorento is on the tow dolly the separate yellow turn signal lamps do not function - the red section of the lamp assembly serves as tail light, brake light and turn signal. The added-on dual-filament bulb is just as bright and functional as the stock bulb.

What I ended up with is a short male plug at the front of the Sorento, which plugs into the added-on short female plug on the tow dolly harness. The tow dolly plugs into the coach, and the towd plugs into the tow dolly. All the lights on coach, tow dolly and towd operate simultaneously. The flasher unit on the coach works fine with the additional load.

Amazon.com: Blue Ox BX8869 Bulb and Socket Tail Light Wiring Kit: Automotive

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Re: Tow Lights Wiring Question

Reply #21 – September 10, 2014, 02:14:25 pm

Chuck, that is exactly what i have done on most EVERY vehicle I tow or have towed. Added another dual bulb inside the tail light lens. S-10, MDX, Ford Ranger. They all had plenty of room inside to add the press-in metal sockets that are easily found on ebay. I got a Magnet light kit from the swap meet for $12 (new) and took its bulbs and wires and ran them underneath. The cost of the wires, connectors and bulbs would have been more than the $12, and now I have 2 extra magnets and housings for the next project that comes along. I know diodes work, but in that infinitessimal possibility that they might fail, this has been a much better solution to me.

Re: Tow Lights Wiring Question

Reply #22 – September 17, 2014, 06:28:48 pm

To close out this thread with a happy ending, I will show the final product. Photos below. Once I got the tow dolly hooked to the coach, and the car on the dolly, it became apparent that I had a problem with the coach trailer connector. I initially thought it was working, but later discovered the "Brake Light" function was not working. Turns out the prior owner used a "custom" 7-pin round connector for his enclosed trailer, which had separate tail light-brake light units, and turn signal units. In other words, a "3-wire" setup. I needed a "2-wire" setup, with a standard flat 4-pin connector. Long story short, I had to add a powered taillight converter to the coach.

Once I had that installed, everything is good! Tow dolly plugs into coach, Sorento plugs into tow dolly, all light work in unison. We're ready to travel!

Amazon.com: Hopkins 46255 Power Taillight Converter: Automotive

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Re: Tow Lights Wiring Question

Reply #23 – September 17, 2014, 07:16:05 pm

Hi Chuck,
I'm glad it all works well. Enjoy the trip. Nice looking rig.
Raymond

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