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Roadmaster 6-Diode Universal Wiring Kit Installation - 2014 Ford C-Max

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How to Install the Roadmaster 6-Diode Universal Wiring Kit on a 2014 Ford C-Max

Today in our 2014 Ford C-Max we'll be installing the Roadmaster 6-Diode Universal Wiring Kit for Towed Vehicles with separate brake and turn signal wiring, part number 154-792-118158. The reason for the additional diodes and the converter box is so that when the towed vehicle uses its brake and turn signals, they will operate independently here on the C-Max. To begin our install we'll go ahead and open up the rear hatch. We've already gone and put our back seats down. While it isn't required, it does give us a little more working room. Next we're going to remove the rear cargo cover and set it out of the way. Then we're going to remove the rear storage compartment door and the fasteners that hold it in place.

Once we remove the 2 top fasteners we'll remove the bottom tray liner and remove the 2 fasteners underneath. I'll go ahead and remove the access panel here. Under the access panel we have one more fastener. Now we can remove the lower tray. To remove it we'll use the flat-blade screwdriver, a plastic pry tool or an interior trim panel tool.

We need to get underneath the tray and release any fasteners underneath. We'll go ahead and set it aside for installation later. Behind the taillight assemblies on each side is an access panel. We'll remove them next so we can gain access to the manufacturer's wiring behind it. Here we can see the manufacturer's wiring harness as it routes directly to the taillight assembly. This will also be where we'll be making the majority of our connection points and installing the diodes for our new towed vehicle wiring kit.

Now that we have access to the wiring, we're going to go ahead and use our test light to locate the turn signal circuit here on the driver's side. With my test light on the 2nd wire down or 2nd pin down on the connector you can see the test light blinking, indicating that this is our turn signal circuit. That'll be a grey wire with a orange tracer. The next wire down is a purple wire with a black stripe will be our brake light. Then our running light circuit is the bottom wire, which is a purple wire with a green stripe. Now that we've identified the wiring here on the driver's side I'll move over to the passenger side and repeat the same process.

So the 2nd pin down on this connector is also the turn signal circuit. That's going to be a green wire. The 3rd pin down is also the brake and that's a purple wire. Then our running light circuit will be the last wire in the connector, that's a purple wire with a green stripe. Now that we've identified all of the wiring on the manufacturer side that we need we can start installing our diode kit. The diode kit is designed to plug inline with the manufacturer's wiring and also with the C-Max and tow vehicle. So it'll have 2 inputs, one from the C-Max and one from the towing vehicle and out will go to the taillight, utilizing 1 set of taillights for 2 vehicles. To make it easier to connect the new diodes, we're going to go ahead and pull the taillight wiring out where we can gain easier access to it. To remove the connector from the taillight assembly, simply press on the locking tab and then pull it out. Now I'll go ahead and disconnect any fasteners that are holding it in place. The fasteners are generally push pin fasteners and can be pried out or use an interior trim panel tool to remove. Now we have a lot more access here to our wiring. Next I'm going to go ahead and remove some of the cloth electrical tape that's around it so we gain access to the wiring and start making our connections. When removing it be careful not to cut the wiring underneath. I don't have to remove it all but we do want to give ourselves plenty of working room. We'll locate the wiring necessary to make our connections. We identified them earlier. The first one was our blinker circuit. It's the green wire with an orange stripe. We're going to take the wire and cut it in half. I'll strip back both ends and add the spade terminals that came with the diodes to either end. Once we install the 2 spade terminals we can install our diode. The diode, again, has 2 inputs, one coming from the vehicle side and the other from the tow vehicle side. Then the out will go to the taillight. Before I actually go ahead and install the diode I prefer to make my other 2 connections. That's going to be the brake light circuit and the turn signal circuit. We'll go ahead and cut those in half and add the spade terminals. With all my spade terminals in place we'll go ahead and make the connections. We're going to stick with color for color because we're just reconnecting the manufacturer's wiring at this time. The only difference is we have a diode in place. Next I'm going to go ahead and get a 4-pole wire. We're going to remove the white ground wire from it and use it for the other 3 connections. We're going to take the 3 remaining wires, feed them up behind the panelling and out through the access hole so that we can start making our connections. This is why we removed the cargo tray earlier, so that we can gain access to this area. 4-pole wiring like this is commonly used for trailers, the brown wire being for running lights and the yellow and green would be brake and turning signal. Working on the passenger side, we'll use the green wire for our turn signal and yellow wire for the brake and then we'll reverse it on the driver's side. We'll go ahead and put the spade terminals on each of the 3 wires now then we can make connections with our diodes. Now with those 3 connections made we'll go ahead and connect it to our diodes. With all my connections made I'm going to go ahead and bundle it up and wrap up our wires with some black electrical tape to help keep them free from dirt, dust, debris and moisture. Then we can go ahead and reinstall it. Secure the wiring as necessary here behind the taillight assembly. Once everything's secured I'll go ahead and reinstall the wiring harness back into the taillight assembly. Now I'm going to move over here to the driver's side and repeat the same process. Note, on a standard install kit with no converter, the running light circuit would be connected in series. However, because we're going to be utilizing the converter and our extra length of wire, we're just going to make our connection at our converter connection. So the yellow spade terminal, which would normally double up as a connection point for 2 wires, won't be used. We're just going to use a standard spade terminal that fits our diode. These can be picked up at any auto parts or electrical supply stores. Here for the driver's side we'll take our added wire with the connectors on it now. Connect the brown wire to the purple wire with a green stripe for our running lights circuit. The yellow wire will be for our turn signal circuit and that's a grey wire with the orange stripe. Then our green wire will become the brake circuit and that's our purple wire. Once all our connections are made we're going to repeat the same process we did on the passenger side, wrapping it up with some black electrical tape and then re-installing the connector. Now that we're finished behind the taillights we can go ahead and re-install the access panels. Our remaining connections will be in the lower cargo area at the rear of the vehicle. We're now ready to mount the converter box. To mount the converter box we'll use a 2-way adhesive provided with the box. We can remove the adhesive and attach it to the vehicle. Note, I recommend to find a location where it's a clean, flat surface and preferably sheet metal. Here underneath the paneling is a great location. It's clean, flat and out of the way. We'll firmly press it into place so we can get a good, cohesive connection. The wire's coming out the driver's side of the box so it's going to the harness then it'll get run to the front of the vehicle and ultimately to our tow vehicle. Here on the passenger side of the box we have 3 wires. The green wire will go to the turn signal here on the passenger side. The yellow wire will go to the turn signal here from the driver's side. The red wire will get connected to the brake signal for both sides. To make our connections we can use the yellow butt connectors that are provided with the diode wiring kit and/or quick supplies connectors, which will allow you to tap in multiple wires onto 1 feed. We'll start here with the passenger side. We're going to take the green wire from our box and connect it with the green wire that we ran earlier up to the taillight assembly. The yellow butt connectors provided with the install kit work for a little larger wires. Instead of re-using a smaller gauge wire I recommend using the Deka 14-16 gauge butt connector, part number 05731-5. As you can see, we've got more length of wire than we actually need so we're going to go ahead and cut the extra length off, leaving just enough that we can move it around as necessary. Strip back our wires and then use our butt connector to attach them. We'll take the yellow wire from the passenger side, route it over to the brake box red wire and attach the two together using the quick supplies connector. We'll slide 1 wire to the inside groove and the other wire will sit on the outside groove. Then we can go ahead and crimp the connection point and close the clasp. The brown wire here on the passenger side we're going to leave it at this time. Move over to the wiring that we routed for the driver's side. Starting with the yellow wire, take it and attach it to the yellow wire that comes off the passenger side of our converter box. We can cut off the excess, strip them both back and use our blue butt connector to secure them together. Then the green wire that comes from the driver's side is, again, our brake signal circuit. We're going to attach it to the red wire that comes out the passenger side or is our stoplight circuit. Since it's our 2nd final connection here to the red wire, what I can do is cut off the excess, strip back both sides and use our butt connector to secure it. To this point we've got both of our turn signal circuits completed and we then ran the brake signal circuits from both sides and made those connections. Our final connections is going to be the 2 brown wires that we routed for the running light circuit. We'll need to get connected directly to the 4-pole harness that'll get routed to the front of the vehicle and connect with the other 3 wires coming out of the driver's side of our converter box. With our new 4-pole harness both ends have a connection point. We need to route the wire inside so we can make a connection with the wires that we've already previously run. To get inside we're going to utilize the manufacturer's grommet here in the bottom of the floorboard. We don't need the plug on this end so we're going to go ahead and cut it off. I'm making a small slice in the grommet. If you're having to push it in like that, it's okay, we can take the grommet down and out. We'll just set it against something solid and make the slice in it that we need. Before I put my 4-pole through the grommet I'm going to take the wire loom that's provided with the install kit and slide it onto the wires so that we can use it later. Beading the wire loom over the wire just makes it easier to install. Once the wire loom's in place, go ahead and push the 4-pole through the grommet and then feed it up into the body of the vehicle followed by the grommet because we'll re-install it from the top down. We'll go ahead and move back to the rear cargo area and finish making our connections. The easiest way to gain access to our 4-pole wire when we put it inside is to remove the foam insulation, grab hold of our 4-pole wiring and pull it up so we're getting access to it. I'm going to go ahead and push the grommet back into place. Following the manufacturer's wiring behind the panelling here, go ahead and route the 4-pole into position. Now I'm going to go ahead and split the 4 wires, strip them back and start making our connections. The 3 wires that come from our converter box they're all plenty long so we're going to go ahead and trim them back. Then we'll strip them and add them to the butt connectors. We now have 3 wires remaining. We have the 2 brown wires that came from the taillights and the 1 brown wire that goes to the 4-pole harness. Here we're going to use one of the yellow butt connectors provided with the diode wiring kit. We're going to take the 2 taillight wires, strip them back, twist them together and then the other side will get attached to the 4-pole harness. Before I wrap up my wires I'm going to actually back up to the ground wire. We're going to take that white wire connection back apart. I strongly recommend to add a pigtail that'll go directly to the ground here at the back of the vehicle so that it's grounded at both the tow and towed vehicles. To ground it we'll take the white wire that we just cut off from the excess. Go ahead and twist the two together and then use our butt connector to secure them. Slide our butt connector on the other side, crimp it down. We'll take the other end of our pigtail and we'll use the ring terminal that's supplied with the 4-pole wiring harness and diode wiring kit and install it on the other end. Now we can remove the manufacturer's ground here, install our ring terminal and then re-secure the ground stud. Now that we have our ring terminal installed, we'll go ahead and put the ground stud back in place. Now with all our connections made we're ready to go ahead and wrap it up with some black electrical tape. This help to bundle up our wires, clean up our installed looks and also to keep our connection points clean from dirt, dust, debris and moisture. Then we're ready to re-install our interior trim components. Let's go ahead and get our 4-pole harness routed into position. Keep in mind when routing any of your wires, stay away from moving components such as steering or suspension, or excessive heat such as exhaust. Now with our 4-pole wiring harness run to the front and secured, that'll complete the install of the Roadmaster 6-Diode Universal Wiring Kit for Towed Vehicles with separate lighting systems, part number 154-792-118158 for our 2014 Ford C-Max. .

Info for this part was:

Employee Joe V
Test Fit:
Joe V
Employee Nicholas E
Test Fit:
Nicholas E
Employee Randy B
Test Fit:
Randy B
Employee Zack K
Video Edited:
Zack K
Employee Sue W
Video Edited:
Sue W
Employee Andrew L
Video by:
Andrew L
Employee Alan C
Video by:
Alan C
Employee Chris R
Video by:
Chris R
Employee Cole B
Installed by:
Cole B
Employee David F
Installed by:
David F

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