First of all, a little history. We have a bike rack mounted to a hitch adapter on the back bumper of the trailer. This is a pretty common setup. The problem is that with the way our trailer’s tail lights are mounted, they are blocked fairly well by the bike tires. We’ve been planning on putting a cover over the bikes to protect them better when we travel, but noticed that a cover would block the lights even more.
Bikes blocking the tail lights
Malcolm bought a pair of surface mount stop/turn/tail lights from O’Reilley Auto Parts for about $7 each. He started by loosening up the existing tail lights and tapping into the wires behind them. For now, the new wires run down the outside wall toward the bumper. Malcolm covered them temporarily with some Gorilla tape. (Update: Later on, he bought a fish tape and re-ran the wires inside the wall and out the bottom of the trailer.)
Tail light package
Temporary coverage solution
With the wires ready, Malcolm drilled holes on the face of the bumper for the screws that hold the light on and a hole for the wires. He drilled another hole in the other side of the bumper to run the wires from the existing lights.
Drilling holes for the light
Drilling hole for the wires
The wires from the light were stuck through the hole on the back side of the bumper and the wires from the existing light were stuck through the hole on the front side of the bumper. The light was then mounted to the bumper with the screws provided.
Wires from the trailer
Wires from the light
Light base mounted
With everything mounted, Malcolm twisted the wires together inside the end of the bumper. Then, moving to the front of the trailer, he shorted out the pin for the running lights to the 12V supply on the trailer connector. This turns on the running lights. Everything lit up as expected. Malcolm also did each turn signal to make sure those were working, as well.
Wires twisted together
Wiring the two top terminals lights up the running lights.
It works!
Malcolm put everything back together except for the bumper end caps. We ended up having to run to WalMart after dinner to get some wire nuts to officially terminate the connections inside the bumper. Since it was dark when we got back, Malcolm will finish that up in the morning.
Final Test
Traveling Talleys 
You can use a standard turn signal flasher to short out the running lights. It fits perfectly! I carry one in my glove box for three reasons: One, it makes it easier to check the lights in bright sunlight. Two, when friends need to find me in a large park at night they can call when they get there and I plug it in and my Big Country becomes a flashing sign. And finally, it could be used to provide emergency flashers if I needed to leave my RV on the road.
Your Random Rover, Gordon
Good ideas. Thanks for the info.
That looks great!! You are so handy š