Mustang Mach-E trailer wiring guide

I recently installed a TorkLift central hitch. I had previously installed one on a 2015 Volt and found it to generally be of high quality. It’s one of the few options currently available for the Mach-E, and seems to have the highest tongue weight rating (500 lbs) which is great for my bike rack and Thule cargo carrier. The install generally went fine, and I won’t go into the details as the providing instructions are generally good. The one thing I will note is that the process involves fishing 1/2″ diameter bolts through the frame of the vehicle to be attached to the hitch. I had to do this in the prior Volt install as well. Not a big deal in and of itself, except the heads of the bolts just barely didn’t fit through the hole identified to fish them through. I ended up having to grind a very small spot on the edge of each of the 4 bolts so I could successfully fish them through the opening without resorting to using a hammer. My recommendation is that the installation cost to have a mechanic do the install with the benefit of a lift and not car ramps would be well worth the 1 1/2 to 2 hours of labor it would likely cost.

Spoiler Alert! The finished product.

With that out of the way, one advantage of doing the hitch install myself was that I was able to fish the 4-wire pigtail for the trailer connection from the bottom of the truck to the underside of the car and zip-tie it to the hitch. In the past I’ve stowed it in the trunk and let it hang out the back through the trunk seal, which is probably a bit less than ideal. Since I had to remove the protective cover from the underside of the rear of the car, I was able to easily run the wire right to the hitch instead. More on that below.

DISCLAIMER: I provide no guarantees implied or otherwise that the procedure below is safe, accurate, or optimal. You could cause damage to your car, injury to yourself or others, or void the warranty on your car. Follow this guide at your own risk!

Trailer light wiring harness: There are a lot of options that should work just fine. I had a Curt wiring adapter I had previously used on a Chevy Bolt, so I decided to be thrifty and reuse that one. It is labeled S0642P-RB I believe, and I had originally ordered it on Amazon, but it appears to be on eTrailer.com as well. I’ve had good luck ordering from both sites. If you prefer not to splice into wires, there are some fancier and more expensive adapters that use sensors that attach outside the wires available as well. I’ve never tried those, so I cannot confirm that they work with the LED lights on the Mustang.

Part 1: Taking the trunk apart

Clear out your trunk, removing any mats and the floorboard that provides access to the recessed storage area where the tire pump is located, and perhaps your portable EVSE / charger.

Now remove the foam insert. Refer to image 1-1 below.
A) Remove the two plastic retainer screws/clips that are located at circles 2 and 5. Circle 1 shows a clip removed from one of the two openings. You’ll notice there is a notch in them similar to a flat-blade screw. Use a flat-blade screwdriver to gently rotate the clips counter-clockwise to loosen them and remove them. Keep the clips with the foam for safe keeping and set them aside out of the way.

Image 1-1: Removing the foam insert and clips from hatch area.

B) Now use a flat blade screw driver or plastic pry tool to pop open the plastic flap shown in circle 3 above. Pry from the side closest to the hatch opening and it will hinge open from the back. This will expose a Torx 25 screw. Use a T25 bit or screw driver to remove the screw. Remove the clip assembly and screw and keep in a safe place for reassembly. Repeat the process for the second clip.

C) On the inside of the trunk on the same piece of trim you just removed the two clips from, there are two more screws. See image 1-2 below. Use an 8mm socket to remove these two screws, being sure to keep them in a safe place.

Image 1-2: Inside edge of the trunk showing two more retaining screws.

D) Next, remove this plastic trim panel. It is held in place still by 6 clips which will release with some upward force on the trim panel. See Image 1-3 to get a sense for where the 6 clips are located on the panel (see the red circles) and where they attach to the car (red ovals). I find that knowing the relative location of the clips makes it easier to know where to pull or pry if needed, as well as knowing what type of clip you are encountering.

Image 1-3: location of clips and corresponding holes on rear hatch.

E) Next, we’re going to pull-back the passenger-side trim panel in the trunk. I’m going to start with pictures of it already removed so you can see the location and type of clips used to hold it in place. See image 1-4 and image 1-5 below. I used a plastic pry tool to get under the rubber seal and pry the plastic panel from the side of the car close to the clips (Image 1-6). I used a pry tool with a “V” on the end to help pry the two yellow plastic clips (Circle 2 in image 1-4, and circle 3 in image 1-5) just above the black circle (see also image 1-7 with pry tool). There is effectively a notch there that looks like a yellow wheel at the top of the clip that you can use to help pry it out without putting too much pressure on the trim panel attachment point. That said, you’re probably fine just trying near the clip too, but YMMV.
In Image 1-5 you will see the power connector that feeds the 12v accessory plug in the back of the car. On the bottom of the gray connector (circle 9, where the red arrow is pointing) there should be a tab you can press in to release the latch on the connector, and then pull the gray plug firmly away from the yellow receptacle. You don’t need to completely remove this panel. With some minor annoyance, you should be able to work in the space here to fish some wires from the tail lights in later steps of the process.

Image 1-4: First two clips on the passenger-side side-panel, starting from the bottom and working our way up.
Image 1-5: Next 6 clips on passenger-side side-panel (circles 3-8) and the 12v accessory plug (circle 9).
Image 1-6: prying the side panel from the car, past the rubber hatch seal. Peak inside, with a flash light if needed, to better locate where the clips (and therefore the pry points) are located.
Image 1-7: Using a pry tool with “V” shape on the end to pop loose the two yellow plastic clips.

F) Not really a process step, but for the curious, image 1-8 shows what the inside of the passenger-side hatch area looks like with the side panel pulled back. If equipped, you will see the Bang & Olufsen Amp and Subwoofer here… or a blank space where you can store your regret if you don’t have them. 😂

Image 1-8: Inside passenger-side panel of hatch area where optional amp and sub may be located.

G) Repeat the process for the the driver-side side-panel in the hatch area. The process is essentially identical, with the retaining clips being mirrored on that side. Behind the driver-side panel the view is a bit different. In image 1-9, you can see another amplifier, which I assume is for the other 9 B&O speakers in the doors and dash. I expect the other amp is just for the subwoofer, but perhaps it’s not that straight-forward. There are also what I guess to be some miscellaneous BCM (body control modules) that may control things like the lights. I did try pulling one of the plugs on the upper module as it looked like it may route to the rear tail lights, but it didn’t have any impact on the lights, and I didn’t want to do anything more that might cause errors in the system. I suspect there is probably a pigtail somewhere that you could plug into for trailer lights that would make this process 10x easier, but don’t know. I’m assuming if there is a factory wiring option in Europe, they probably have a module that just plugs in somewhere without having to tap wires.

Image 1-9: Behind the driver-side panel showing another amplifier and probably a couple of BCMs.

Part 2: Placement of the trailer wiring converter box, grounding, and running the pigtail

You can pretty easily locate the converter on either side of the car. There are some nice bolts to use for the ground on both sides. The passenger side has the 12v accessory receptacle which seemed like the obvious place to tap for power. However, with the large amplifier and subwoofer on that side, and the grommet I used to fish the pigtail under the car being closer tot he driver’s side of the car, I elected to mount/zip-tie it on the driver’s side.

H) There is a screw hole on this for mounting, so you could remove a nut from one of the existing brackets and secure it there. I elected to just zip-tie it to some nearby clips and harnesses. See image 2-1, circle 1 for location. I then removed the bolt in circle 2 and added the negative/ground wire and reattached the bolt. I believe that was also an 8mm socket size.

Image 2-1: Finding a location for the trailer light converter.

I) With both side-panels loosened up, you can pretty easily lift up some of the carpeting to expose a few rubber grommets that allow passage to the under-side of the car. In previous vehicles I just stowed the cable in the trunk and draped it out the back of the hatch, hoping the rubber seal around the hatch had enough give that it wouldn’t crimp a wire. It was never an issue, but I think the “correct” manner is to route it to the underside of the car and attach the pigtail plug next to the hitch. I found a circular grommet large enough to allow the plug at the end of the pigtail to pass through. I then cut a notch in the grommet and re-inserted it. It may be better to cut an “X” shape in the grommet, leaving the outer lip intact. Your call. Image 2-2 shows what this looks like from the underside of the car. Note that you need to remove the under carriage protector to get at this, which is a bit of work, but I already had it off to install the hitch. However, if you already had the hitch installed, you don’t need to remove the entire weather guard…

When running the trailer connector out the bottom, there is an access panel underneath that only takes 3 bolts (instead of removing the entire weather guard). This wasn’t an issue for you because you had the weather guard removed to install the hitch.

Thanks to Jeffrey Michael for the note.

I won’t cover this in detail at this point, as it’s covered in the hitch documentation. I may add detail later for those that may want it. Image 2-3 shows the connector and end of the pigtail being zip-tied to the hitch. I secured it with a tip-tie on the top of the frame of the hitch as well to prevent it from moving around over time.

Image 2-2: There are a couple of rubber grommets in the well of the trunk. This one was toward the driver side and was large enough to fit the connector for the trailer wiring pigtail through. I cut a notch in the grommet and placed it around the wire, securing it with some duct tape above to prevent the wiring from shifting.
Image 2-3: I then zip-tied the pigtail to the hitch. I zip-tied it about a foot further up the wire to the top of the frame of the hitch as well to keep it from moving around under the car or rubbing on something over time.

Part 3: Tapping into 12V power and the four light connections

First, some background:
So this is the fun part where I got to use a multi-meter to test lots of connections with the turn signals on, running lights, brake lights, hazards, etc. to identify which wires did what on the rear lights, as well as validating which connection on the 12V accessory outlet was positive. We did the ground connection already, and we’ll cover the 12V connection in this section. The four other connections are:
1) Left turn signal
2) Right turn signal
3) Tail lights (or running lights)
4) Brake lights

You obviously need to tap the left turn signal from the driver-side side lights and the right turn signal from the passenger side lights. The tail lights and brake lights are available on both sides, so you have some flexibility. Based on whether you located the wiring converter on the driver side or passenger side, that may dictate which side you tap for the brake and tail lights to minimize running wires across the width of the car. In my case I didn’t worry about that too much as I had plenty of wire, and I thought it might be good to run two wires per side, as the grommets we will pass the wires through are pretty small, but I think 3 wires would fit through OK. There isn’t really a wrong answer here. You can follow what I did, or adapt a bit to suite your needs. Once you know the pin-outs to tap into, it is pretty straight forward.

The LED lights on the back of the car are held in place with two screws and some pressure fittings, and just pry out once the screws are removed. Both the left and right side have identical 8-pin connectors. The receptacle the lights plug into is mounted low and tight to the body of the car (See image 3-1). I didn’t want to pry it out, or get into removing the bumper, so I elected to tap the wires running from the LED tail lights to the connector. Ultimately it would be nice to get the male and female connectors and make a plug-in harness, so tapping wires is not needed. I’m assuming those aren’t readily available.

As an aside, the plug on the LED module was labeled “33472-4801” and on the next line “20060 26” if that helps anyone. Not sure if that’s for the plug only, or references the entire light module.

So be ware, if you make a serious mistake tapping the wires, worst case you may be looking at replacing an expensive LED light module. I had no issues, but again, proceed at your own risk.

Image 3-1: Recessed 8-pin receptacle for rear LED light modules.

Looking at the plug on the light modules, here are the pinouts based on my testing with a multimeter (reference image 3-2 and table 3-3).

Image 3-2: the pinouts on the LED light enclosures.
Pin #FunctionWire Color (YMMV)
1Tail / running lightBrown
2Stop LightRed
3Steady 12VN/C
4 Turn signal (RT / LT)(Yellow / Green)
5Steady 12VN/C
6Ground ?N/C
7Ground ?N/C
8Ground ?N/C
Table 3-3: Mapping of pinouts to function and wire color, though wire color may vary depending on the make and model of your wiring converter. Thanks again to Jeffrey Michael for pointing out I had originally reversed the pinouts above.

I) Now to remove the left and right light enclosures so we can get to the wires we need to tap into. There are two 8mm screws under plastic caps on both sides of the car under the tailgate opening. Use a pry tool or very small screw driver to pop out the four plastic caps (two per side), being careful to keep track of them. See images 3-4 and 3-5. Next remove the four 8mm screws, again, two per side.

Image 3-4: one cap removed, showing location of tabs that hold it in place (top and bottom).
Image 3-5: showing where to use pry tool to pop off plastic covers to access screws for rear body-mounted LED lights.

J) With the screws removed, you can now carefully pull on the light enclosure to remove it from the two pressure fittings on the rear of the enclosure. I found that it helped to carefully use a plastic pry tool on the outside of the enclosure with one hand while pulling outward on the enclosure with my other hand from the opposite side. See images 3-6 and 3-7.

Image 3-6: Popping the LED enclosure out of the pressure retaining clips in the back of the housing.
Image 3-7: You can see the two rubber receptacles and corresponding metal prongs in this image that are held in place by pressure and minimize vibration.

K) Referring to image 3-7 above, while holding the LED enclosure with one hand, use your other hand to follow the 8 black wires to the the plug. There is a plastic latch you need to depress on the side of the plug facing the back bumper of the car. Depress the latch and firmly pull the plug from the receptacle. Repeat the process for the other side.

L) There is a small rubber grommet on the body of the car, above the two rubber fittings that held the LED enclosure in place. Remove these from both sides. You’ll need to cut a slit in these so you can feed the wires we’ll be using to tap into the LED pigtail into the side panel of the car, and ultimately to the trailer wiring converter. Refer to image 3-8 below.

Image 3-8: Rubber grommet to be used to feed wires from LED light enclosures into side panels of car.

M) You’ll need to tap the wires on the LED pigtails according to the diagram above. I labeled the wires and verified the pins as it can be confusing mapping from male to female plug sides, and then from the front to the corresponding wires. Here are the wires corresponding to pin 1 (turn signal on right side) and pin 3 (brake light) in image 3-9.

Image 3-9: close up of the passenger side light enclosure pigtail showing the labels on the wires corresponding to pins 1 and 3.

N) I found that the blue wire taps people love to hate will not work with these black wires on the LED enclosure. They are two small for the metal blades to fully pierce the plastic coating on the wires, so no electrical connection is made. Instead, I used wire strippers and carefully exposed a small section of wire about 3 inches away from the plug. I then twisted the wire I’d be using to tap around that exposed section, and then used a small amount of solder to secure it. See image 3-10 for an example. This should eliminate any possibility of a failed connection in the future. However, it’s also not cleanly reversible. Next, trim the excess wire after the solder cools, and use electrical tape to insulate the connection.

Note 1: I used wire matching the gauge of the trailer wiring module and then used wire butts to splice them together. This made it easier to solder the wires to the LED modules in my garage, not in a tight space inside or around the back of the car. If the wires with the wiring module are sufficiently long, you may not need to do that extra step, but you’ll need to fish the wires from inside the car out through a very tiny hole, which will require another wire to fish them through. If you go this method, REMEMBER to fish the wires through the car and through the rubber grommets before soldering. See step O next.

Note 2: Ensure the length of the wires you use to tap into the LED modules is of sufficient length to reach the intended destination. If your trailer wiring module is located on the opposite side of the car from the light you are tapping into, then you’ll want several feet of wire to make that connection as you’ll need to run under the carpet in the trunk to the other side-panel.

Some people elect to get more expensive trailer wiring converters that use sensors to detect the signal in the wires, rather than an electrical connection, which doesn’t require piercing the protective coating on the wires. You could go that route if you so chose.

Image 3-10: wires tapped by exposing some of the plastic coating on the wire, and solder the tap wires in place.

O) Now that you’ve soldered the wire taps to the LED modules, you’re ready to run the wires through the rubber grommets and then fish them through the side panel of the car. See image 3-11 below.

Image 3-11: Running the wires through the grommet and fishing them into the side-panel of the car.

P) Leave enough length of wire between the grommet and the LED module to make future removal easy and to avoid blocking any of the rubber fittings that the enclosure needs to seat into. Do not leave much excess wire as it will be more likely to get caught or crimped on something. Plug the LED module’s plug back into the corresponding receptacle on the car. Route the wires away from the fittings and press the enclosure back in place. See image 3-12.

Image 3-12: Plug in the LED enclosure and route the new wires out of the way of the pressure fittings.

Q) Repeat the process for the other LED module and other side of car. On the driver’s side of the car, I routed the wires out through an opening beyond the amplifier (Image 3-13, circle 1) and then zip-tied them to existing wire harnesses (Image 3-13, circle 2 and below).

Image 3-13: routing the wires from the driver’s side LED wire taps.

R) On the passenger side of the car, I also routed the wires behind the amplifier on that side, and zip tied them to existing wiring harness to prevent the wires from making contact with the amplifier. I noted that after listening to music while I was working on the car for a while, the amp got really damn hot! There are vents on both sides of the plastic side-panels to help with that, but no fans of course, just passive cooling. See the two circles in image 3-14 for an example.

Image 3-14: routing the wires from the passenger side LED wire taps.

S) The last tap to make is for 12V power for the trailer wiring converter / module. For this you will want to tap into the purple wire feeding the 12V accessory port in the back of the car. See image 3-15 below, and recall images 1-5 and 1-8 where this connector was first identified.

Image 3-15: tapping into the 12V power from the accessory port in the hatchback area.

T) I then taped the tap wire along the existing power cables, and met up with the two wires I had run to the LED modules. I then taped these together and routed them behind the insulation on the side of the car, to keep them from rubbing on the side panel when it gets reattached. See image 3-16 below, with two areas circled in red.

Image 3-16: routing the power tap wire and light tap wires down the side of the car and under the carpet to meet up with the trailer wiring module on the opposite side.

U) Connect wires as needed between the taps you made and the trailer wiring harness. Use zip ties and electrical tap to keep wires from rubbing, shifting, or getting damaged from crimping when panels are reattached. See image 3-17 below for the fully wired trailer light module on the driver’s side of my car.

Image 3-17: fully wired harness is in place.

V) Before you put all the side panels back into place, connect a trailer to your pigtail connector and/or use a tester to ensure everything is working as expected. See image 3-18. Be sure to test: left and right turn signals, running/tail lights, and brake lights. Brake lights will show as left and right both illuminated on a tester. Tail lights require that the headlights be on, so during the day you need to adjust the headlight selector to be in the ON position and not Auto.

Image 3-18: Test the functionality of your new installation before reattaching all the side panels and trim pieces. I’m an optimist, but still!

W) After a successful test, you can now start the process of putting all the panels and trim pieces back in place. You should be able to follow the directions above for disassembly in reverse, making note of the location of clips and aligning them before pushing on panels and trims to secure the clips back in place. I used a trim removal tool to help put the rubber seal around the hatch opening back into place as I worked my way along the panels and trim. Move the rubber seal out of the way before trying to reattach clips in the vicinity. See image 3-19.

Image 3-19: move the rubber seal out of the way as you reattach panels and trim pieces.

Let me know if you tried the process and if this guide was helpful. Feedback, corrections, and improvements on the process are welcome.

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