Converting Side Marker Lights to Turn Signals

Early on when driving our 2022 Georgetown GT7 motorhome I was surprised how no one gave me any space to change lanes while driving in traffic. Yes, I know people are just that way sometimes, but in my experience most people are pretty courteous with allowing you to move over when your pulling a trailer or driving a large vehicle such as a motorhome, and this was disturbing to me. So I did a little investigating and determined that people driving next to me in our 35 foot motorhome have no idea of my intentions to change lanes because there is no visible turn signal on the side of our coach, just three static marker lights and no turn signals in the side view mirrors. This was a plus for humanity but I knew I had some work to do.

First let’s discuss a little background on automotive lighting. Traditionally a light on your vehicle that has two functions, such as a taillight that doubles as a turn signal, has three wires – one ground and two hots. One hot, in this example, would feed the running light function and the other, the turn signal function. With incandescent bulb these two light functions would operate in what is called a single double filament bulb. In newer LED lights, one hot lead would go to one bank of lower brightness LED’s and the other would go to a different bank of brighter LED’s.

With an understanding of how these lights work you’ve probably already guessed that your side marker lights, if like our Georgetown, are two wire lights rather than 3 wire lights. It’s also somewhat disturbing to note that there is no regulation in the US, as there is in other countries, to have visible turn signals on the side of any vehicle. So how do we fix this problem and convert these single function side marker lights to dual function side marker and turn signals? There’s actually two potential solutions. Let’s first cover what I did.

I felt it was simpler to just change out the two-wire LED side marker lights on our Georgetown with 3-wire LED lights. I wanted to find something in a similar size, which was about 4″ x 2″. This ended up harder than I thought but I did find lights that were just about a 1/4″ longer and a 1/4″ narrower then the originals. When I received the lights I was very impressed with the quality. They are a sealed lights so no moisture is going to get in, as opposed to the OEM lights which are plastic, these have a nice aluminum backing and came with a foam insert that goes between the light and the side of the coach. So, let’s get to work.

1. Remove existing lights: Remove existing side marker lights on the passenger side of the vehicle by removing the screws and cutting the wires just past the butt connectors. Remove all old caulking with an adhesive remover. I like to use WD40 for this. Once all residue is removed, clean the surface with a vinegar/water mix.
2. Install backing: This might be the hardest part, but is only required if the surface behind the marker lights is not painted. Cut a piece of 2″ wide black automotive vinyl tape (used for pinstriping and such) at the exact length, or slightly shorter, of the new marker light. carefully round the edges with some good scissors. Then attach the tape to the surface of where the old marker lights were, being sure to cover the unpainted surface.
3. Run new wire: Run a red 16 gauge insulated twisted copper wire from the rear marker light up to the front of the coach near the front passenger headlight assembly. You can either insert the wire into the existing wiring harness split tubing our simply attach to the existing wiring with zip ties. Either way, secure the wire well and avoid coming in contact with sharp surfaces or moving parts. Also be sure to leave slack at each of the three side marker light locations. 100 feet of wire was perfect for our 35 foot motorhome, so purchase accordingly.
4. Splice into turn signals: Start at the front and connect the Red wire that you just ran to the right turn signal lead. Connect with blue quick splice snap connectors or other good connectors. You might have to remove the connector from the back of your front turn signal assembly and test with a volt meter to determine which wire to use. Look for the alternating voltage with the turn signal on. On mine it was the Yellow wire for the passenger side and the Blue wire for the drivers side.
5. Connect new side marker lights: Using waterproof butt connectors attach the White wire of the light to the White wire that was previously connected to the original light. Then, connect the Black wire of the light to the other wire that was previously connecter to the original light with a butt connector. Finally, cut the new Red wire (front and middle side marker only) so you have two ends. Connect these two ends along with the Red wire from the light with a closed end crimp connector. Connect the rear side marker the same way, but since its the end of the run you will only have the two wires to connect.
6. Test the lights: Before you permanently attach the lights I recommend testing the lights first. Turn the ignition to the on position then turn your parking lights and right turn signal on (cautions, steps will come in if your door is closed). All three side marker lights should alternate between low brightness (running lights) and high brightness (turn signals). All turn signal lights should work in unison.
7. Attach the lights: Carefully align the lights so that there is an equal amount of black tape above and below the lights, then mark the two screw holes. Carefully drill pilot holes in the marked location. Attach with existing screws but first apply some silicone in the holes and on the screw threads. Alternately you can use black decorative screws or paint the screws black.
8. Final step: Fully secure and tape all wiring so that it does not sag or rub on any surfaces. Then, test the lights once again as you did in step #6.
9. Drivers side: Duplicate these steps for the drivers side but now splice into the drivers side turn signal lead.

This is the list of all items used for the above modification. Click on the links if you wish to purchase any of the products:

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Although not thrilled with having to use the backing tape, I was very pleased with the outcome. The lights are so much brighter than the original lights and the turn signals work! On our first trip with the new lights, driving into Las Vegas, I had a chance to test the turn signals twice when needing to change lanes. Both times the vehicle next to me slowed down and let me in.

There is one alternate solution to converting your side marker lights to dual function lights which I did not try. It involves using an adapter made for Daytime Running Lights (DRL) modification for older vehicles not equipped with DRL. There’s a great article from an individual who I got in contact with. The biggest challenge I saw with this option is the need to separate the identification and clearance lights on the front and back caps of the motorhome so that they don’t flash as well. I just wasn’t sure how our motorhome was wired and didn’t want to get into that. However, I also didn’t realize at the time the extra effort I would soon encounter with replacing the side marker lights.

Overall this is a worthy modification for your motorhome and, in my opinion, should be a NHTSA regulation for all vehicles over a certain length. Feel free to drop us a note if you have any questions.