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Installed a hitch and wiring harness on my M3
- Thread starter xpitxbullx
- Start date
Just installed my Eco Hitch and looking into wiring harness solutions. Can you provide any more details on how you wired this up? Did you directly solder to the existing wires? How did you determine which wires did what?
android04
Active Member
I don't know what specific wiring harness xpitxbullx used, but I tried a simple non-powered Curt trailer light harness. I had it lying around for 5 years and figured I would try it. It was marked that it was compatible with LED lighting, but it was not compatible with the PWM signal that Tesla puts out for the brake lights. So my running lights and turn signals would work, but brake lights would only pulse on once and go off.
So I purchased this ModuLite Wiring Harness Kit #119190KIT Upgraded Heavy Duty ModuLite Circuit Protected Vehicle Wiring Harness with Installation Kit Tekonsha
This works perfectly, but you have to splice into or tap into the taillight wiring. I used the smallest PosiTaps (Red in color, for 20-22 AWG wire) www.amazon.com/dp/B001MPW54G/. I ran the power wire from the battery through the interior of the car (all along the bottom passenger trim all the way to the trunk). I grounded to the same chassis bolt that the subwoofer/amplifier in the trunk use.
Here is the wiring color and function for the Model 3 taillights (keep in mind that my car was made in March 2018 and yours may be different):
Passenger side: Red = right turn, Yellow = lights, Grey = brakes
Driver side: Purple = left turn, Pink = lights, Grey = brakes
P.S. Another possibly easier and safer alternative to the wiring kit I posted above is the ZCI Circuit Protected Wiring Harness Kit #119250KIT ZCI Circuit Protected Vehicle Wiring Harness w/ 4-Pole Flat Trailer Connector and Installation Kit T that does not require splicing or tapping into the taillight wires (it has inductive sensors that clamp over the wires). However, it's a little more expensive and I've read a post by one Model 3 owner that it didn't work for him. It was possible that he didn't install one wire correctly or that he didn't use the learning mode correctly, or that the unit was defective.
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SageBrush
REJECT Fascism
Thanks for the reply. Based on xpitxbullx's setup, I went to an auto parts store and got a basic 4-flat universal connector set and planned to tap directly into the tail light wires (like this, but w/ 4 wires: https://amzn.to/2XuAB7C). I used a multimeter to ID the running lights, left and right turn signal. I wired everything up and tested the 4-flat connector to confirm that power was going to the correct pins when lights were turned on. Everything looked good. Unfortunately, when I connected this to my trailer, I had no luck and none of the lights worked.... I understand that running a separate wire up to the 12v battery is ideal, but assumed, when reading the OP, that the power going to the car taillights would be enough to power the trailer LEDs.
I'm not sure how to proceed. I really don't want to spend $100+ on one of the etrailer kits. Any ideas on how to make my setup work? Think I will need to buy a wiring kit w/ a separate power that will need to be run to the front of the car to tap into the 12V battery?
SageBrush
REJECT Fascism
android04
Active Member
Wiring directly to the tail light wires like you did should work, but you need a converter module that comes with most wiring kits because the Model 3 has separate wires for brakes and turn signals. Trailers in the US use the same wire/bulb for brakes and turn signals. The module in the wiring kit combines the signals together.
There are converter modules that are powered by the same circuit that turns on the tail lights and turn signals and brake lights, but it doesn't look like they can handle the PWM signal of the brakes. By the way, PWM means that the signal is not a solid ON or OFF, it pulses ON and OFF many times per second. This is fast enough that the human eye can't see the pulsing, but a lot of cameras can. If you ever saw a Youtube video of a car driving and it's brake lights look like they are pulsing, that's the camera catching the pulses where the human eye would not see them.
If you find it too difficult running a power wire from the 12V battery in the front, you can possibly get 12V from the converter under the rear seat cushion. For details on that, find an "aftermarket sound system" thread on these forums. Some people tap into that for amplifiers and subs.
Wired up everything but the power. Still having trouble finding out if the rear seat 12v dc-dc terminal will be overpowered for my application. Here's a post I made on an aftermarket sub-woofer thread. Aftermarket Sub-woofer Amplifier Installation using DC-DC +12v Power Source
android04
Active Member
I don't think you will have any problems with connecting your power wire (with the 15 amp fuse) to the DC-DC terminal under the seat. There really isn't an issue with being "overpowered". The trailer light harness will only draw the power it needs to function and power the trailer lights. Also, the trailer lights are a very small load compared to an aftermarket amplifier, especially if the lights are LED. I wouldn't worry about any issues.
I tried to follow in your footsteps! Now my signal lights and brake lights don't work…best guess is my trailer overloaded the circuits. Everything I've read, there is no fuse box, just breakers that internally reset after (30?) hours…
I spliced two wires on the left side, doubletapped ground to an existing a chassis screw on left, and 1 splice on the right side. brakes and signal worked after wiring up harness…but when plugged in trailer neither trailer nor car will brake/signal/running light up any more…
Never tested trailer prior to plugging into Model 3. May be wiring fault there? Trailer has incandescent bulbs so perhaps it drew too much amperage from what the car was expecting…
Couldn't find anyone who may have experienced the same issue as me online…doubt the wiring is different in Canada…
Anyone got any guesses, suggestions, pointers, or spare fingers to cross?
Will update when I can figure out more…
android04
Active Member
The smart fuses will probably reset once the car goes to sleep (let it sit for an hour after it stops charging). Try unplugging the trailer plug and make sure that your car's lights work first. If you have a multimeter you can test resistance on the trailer plug between ground and the 3 other prongs. There should be some resistance from the bulbs. If the resistance is close to 0 Ohms, you might have a short in the trailer wiring.
android04
Active Member
Also, I don't know if you used xpitxbullx's description of Slots 1-5 to wire in, but if you aren't using the same locations as he is that can be your problem. You should use an LED test light to probe each wire and have somebody press the brakes or turn on a turn signal to see what the wire you are probing does. Otherwise, double check what you wired with these wire colors that I got from my car:
Driver side wiring: Purple=Left turn, Pink=Running Lights, Grey=Brakes
Passenger side wiring: Red=Right turn, Yellow=Running Lights, Grey=Brakes
Battery fits nicely in the left trunk well, and only put it in when towing. Can post picks once the bikes are off the rack of that's helpful.
Thanks DeepRed,
I like the thought of putting a small battery in the trunk vs. running a wire northward. I don't tow frequently and happen to have a small battery on hand.
And, nice boat! I have an O'day Daysailer.
android04
Active Member
I used the Tekonsha kit 119190KIT that cost me $60. Cost was the main reason I got this instead of the ZCI kit 119250KIT, and also because I'm not afraid of tapping into the tail light wires. Upgraded Heavy Duty ModuLite Circuit Protected Vehicle Wiring Harness with Installation Kit Tekonsha
It's worked fine. I ran my 12v power wire though the interior of the car along the bottom trim and through the firewall using the same rubber grommet that the cabin heater orange wires go through. Passing the wire through that grommet was the hardest part. If I had to do it again, I would probably run the 12v wire to the switched power source under the rear seat (like a lot of the people adding aftermarket sound systems are doing).
It's worked fine. I ran my 12v power wire though the interior of the car along the bottom trim and through the firewall using the same rubber grommet that the cabin heater orange wires go through. Passing the wire through that grommet was the hardest part. If I had to do it again, I would probably run the 12v wire to the switched power source under the rear seat (like a lot of the people adding aftermarket sound systems are doing).
rotus8
Member
DON'T DO THIS! This is actually quite dangerous; If for some reason the hitch receiver pin comes out, your whole rig will separate and the trailer complete with the ball mount will take its own path down the road. The safety chains should be connected to the hitch receiver or car. There are many reports of the pins coming out for whatever reason. Be safe.
I had a local bike rack store install my eco-hitch. They informed me that an auto body shop down the road does the actual work. First question was have you done this before to an M3, yes plenty was the reply. Great, lets do it! Got it back and it looked great. drove around with it for a week or so till I actually put a bike rack on. Looking underneath at the plastic floor pan I saw that they had hacked a hole through the plastic for the 2" adapter to attach to the hitch itself. I see that the Model X has a plastic removable cover for when the attachment is taken of the hitch. The open space on the X when the attachment is on is much larger than the hole that has been cut into my floor pan. My question would be, what are the risks of dirt, water, snow etc getting under/into the space opened up in the floor pan?
Thanks
Thanks