Wiring Harness Installation - 2003 Volvo S40

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Products Featured in this Video

Modulite Lite Trailer Light Module

118187

$39.95

Modulite Installation Wiring Kit

118151

$9.95

Installation of a Wiring Harness on a 2003 Volvo S40

To begin with, all the wiring is in the trunk of the vehicle. Well get into our trunk, take out a couple of the panels in the bottom threshold, and we can see our wiring from there. We have to take out our panels here, you can see the little rivet here that twists a little bit and pops right out. Theres one on each side here and here, which we have to take off too. Once we have our panel out of the way, we have all of our wiring exposed to the drivers side tail light and we also have a nice ground here we can use. Well take apart the other side to get to our wiring, then well test for signals. What weve done here is use a piece of angled iron you can use whatever you want to hold this out of the way. Well test for the running lights to see what wire it is, and what well do on this one is well pull out the socket assembly like so, and as you can see we have our running light on. Well test at these points here to see which wire is what. This wire here is our running light circuit.

We will go ahead and tap into that. You want to double check that after the splice. Now well switch over to the turn signal. It looks like its the blue wire with the yellow stripe. Now well test for the brake signal, which is the green with the red stripe. Now well use this ground screw to attach our ground wire. Next we have to find a safe mounting spot for the box, the flat plate behind the tail light here below it, well attach it there. The only two wires we have to worry about now is the power wire that goes to the front of the vehicle to the battery, and the right turn signal which well run this green wire across to the other side. We have our green wire strung out and theres a wire harness here, well zip tie along that length here and then come to our passenger side tail light. With our right turn signal going, well test for it. Well cut off some of the excess of this wire here. Well install one more zip tie to keep things nice and neat, then well be done with the interior. Since were done with this part we can put this back together. There is a grommet here, or a rubber plug, which goes to the outside. What well do is cut a small slit in it and run our power wire through there, underneath the vehicle and up to the battery. Then well take a zip tie and tie it up in here too. The four pole wire itself actually gets left inside the vehicle, also if you wanted you could run it through that grommet and out the bottom. It would be exposed all the time and if you dont use it a lot its best to keep it inside and only use as needed. We can start threading our wire up to the front theres a nice little hole through the body there and well start with that.

Then we will follow this line going up to the front. Route the way you want temporarily, then come back with some zip ties. Were going to throw it up here over the sway bar and pull it out and through, then well make sure were away from all steering linkages. Looks like we are so well go straight up from here out towards the hinge on the hood up there. I just want to push it up there as far as it can go and the friction will hold everything into place, and well reach down and pull the rest up. Weve pulled it up through and had to make adjustments. We had to re route it so it wouldnt bind up on any lines, we came up through the brake booster here. We threaded it straight up as close as we can to the firewall so were away from any moving parts. Pull them up and come behind this plastic cover here, and zip tie it to keep it into place. Then well work our way up to the battery. At this point well install our fuse holder. Before we make our connection to the battery well disconnect it, by taking off the negative battery lead. Well install our fuse while were here. Make sure theres plenty of leader and it looks like it wont go anywhere. Well put our negative terminal back on. All that remains is putting the battery cover back on and test the system out. As you can see were finished with our install, and we left our wire harness hanging out of the back to give you an idea of how its used, when youre using it, hooked up to a trailer. Again when youre not using it, fold it up and store it in your trunk or spare tire well. That concludes our install for part # 118187 and 118151.