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Hitch harness wiring to accessory vs battery

2K views 9 replies 5 participants last post by  sox343 
#1 ·
I have a 2011 EX no tow package. I put a Curt 13066 hitch on the car, and am looking at harnesses now. I'll be towing under 1000 LBS so I'm not worried about the lack of a towing package.

What is a problem though is that there is no wiring at the back of the car for it. All the harness manufacturers at etrailer.com have a long lead to run under the car to the positive battery terminal. So I have three questions:

1. Is it not possible to drive the trailer lights off the same supply as the tail lights? Why do I need a separate power supply?

2. There is a 12V accessory plug on the rear driver side already. Can I not splice off that? It's hot in run, and I don't expect to be running a compressor while rolling with the trailer.

3. Any tips on running the wire up to the battery? I can't find any good places to zip tie along the driver side. I don't want to put self tapping screws into the sheet metal.

Thanks,
Rob
 
#2 ·
1) Pulling more power off the stock wiring may or may not work, depends on how much current your trailer lights will draw. You may get lucky and installing a wiring kit without battery connection will work for your trailer, or you might not get lucky and have to buy the wiring kit with battery connection and do a second install.

2) Yes, you probably could get away with connecting it there but you won't have any trailer lights when car is turned off. It may not be a problem normally, but I could imagine there are times when it would matter.

3) I don't remember how I ran my wire, but I certainly didn't use screws. It was all zip ties
 
#5 ·
I had my hitch professionally installed and wired with a secondary ECU. This was so there would be no loading of the circuits to upset the vehicle's own computers/ECU's.

Came out one morning and discovered the ECU decided to fry itself overnight, car had been switched off all night and no trailer had been used for at least 3 months:



Luckily there was no other damage to wiring or interiour of the car, still don't know why it melted, it has been sent back to the manufacturer for analysis.

Upside is that even though this happened 6 years after it was installed, they honoured their lifetime warranty.
 
#7 ·
I won't name the brand other than say they are one of the largest aftermarket hitch suppliers in Australia, they did the right thing by me with replacing a 6 year old part free of charge and were very concerned about what had happened with follow up questions from the main office when they received the burnt out ECU. I take it this has not happened with any of there other ECU's and they have sold thousands of them.

I think the problem was a combination of a mistake when it was installed (the installer did not fuse the main lead), the use of IPS electronic circuit breakers that "trip" then reset themselves and thus continuously supply power in a pulsed fashion, and a faulty component on the board. New hitch installs now have fuses and I made sure I installed one on mine as well.

The ECU was installed on the inside of the rear quarter panel about 10cm from the fuel filler. There is no way water can get into the unit. I believe the unit was encased in that black epoxy resin, and that it got so hot it melted the resin as there was a black watery substance that came out of the box when I opened it. Smell was very toxic - like that of those old fluro tube ballast transformers when they used to blow-up.



 
#9 ·
Based on the size of the traces and the package types, I think missing device is probably a power MOSFET. They're handy for DC switches since there's little drop across the junction. The downside is that they do have a thermal runaway failure mode and it probably had a leg on the common +12vdc line. I think there's two vaporized devices and a nasty carbon trail between the diode in the lower right and the FET in the upper left that was hot enough to lift the copper trace and burn the epoxy on top.

Tough to know the root cause vs the innocent bystanders.
 
#10 ·
My hitch and wiring harness was dealer installed. The 12v feed was taken from the under hood power block as shown in the picture. They ran the wire in a plastic loom down the firewall and under the vehicle to the back.
 

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