Bike trailers seldom have tail lights – most times only reflectors are mounted.
I wanted my trailer to be better seen by night without using battery lights.

Your bike should have a dynamo to power the lights.

With a good dynamo there is enough power for two LED- tail lights.

Supplies

You will need:

elastic and sturdy plastic sheet from Polyethylene or PET (You can derive it from old bottles or packaging material…)
Cinch coupling (female) for through hole mounting
Cinch plug (male) with flexible coaxial cable (about 1,5m)
LED- tail light for bike with super cap (will stay lighted at short halts)
Screws for mounting the parts to bike and trailer
Tape to fix the cable at trailer chassis flexible
2-wire cable to connect the bikes rear light to the Cinch coupling (ca. 1m)
common tools

Step 1: Prepare the Parts for the Bike.

Cut out a piece of plastic sheet about 40 x 50mm .

Make one hole for the cinch coupling and another to fix the sheet at the Bike. near the hitch. I used M6 screw and nut so a 6mm bore would be needed. But that depends on your bike.

Temporarily mount the sheet near or on the bikes rear axle .

Mount the Cinch coupling to be sure it does not interfere with spokes, chain or other moving part on the bike .

If the sheet and Cinch Coupling can be mounted as shown, solder the two wires to the Cinch, using the inner contact for the live wire and the outer for ground. Mount Cinch coupling to the plastic sheet.

Step 2: Mount Cinch Coupling to the Bike and Connect Wires

Fasten the plastic sheet to the bike next to the hitch. Wrap the wires around the fender stay up to the tail light and connect it to the wire and ground that come from your dynamo. Make sure your bikes tail light stays connected, too.

Step 3: Testing the Connection

If all parts are mounted correctly you should have the power wire from the dynamo at the inner contact of the cinch and ground at the outer contact.

Now you will need a helping hand to turn the wheel, driving your dynamo and test the connection.

Put in the Cinch plug with coaxial cable connected and connect the new LED- tail light that you will later mount to the trailer to the other end. Test if there is power when the dynamo turns . The tail lights of bike and the one at the coaxial cable should both be on.

Step 4: Installing Tail Light at Trailer

Attach the trailer to the bike, put in the Cinch-plug and fasten the coaxial cable at the trailer hitch, leaving enough loose cable that the trailer can move without pulling at the plug .

Fix the cable to the trailer hitch with tape and wrap it around the tubes of hitch and chassis towards the rear side of the Trailer.

Fasten the tail light to the trailer (I used some aluminium sheet as a platform for the tail lights) and connect the cable.

Once more, test if all the lights are on when the dynamo turns quickly.