Installed today. Everything fit nicely and works properly.
For anyone interested in changing over to LED:
Any of the oval style Optronics LED STL series brake lights I believe (look on website to make sure) are a direct swap with the original ones on the trailer. All you need are the lights themselves. The grommets and pigtails aren't necessary. Unplug the lights from the underside of the trailer. Push from where the wires plug in and with a little help with a screwdriver, pry the light out from the grommet. Once you get it started it should slide right out. Leave the grommet in place, plug in new light and slide back in. The only thing that keeps the brake lights in place is compression from the grommet itself.
The 5 red markers that are linked above are a direct swap also. The lights pop off with the help of a small flat bladed screwdriver. Be careful not to break the plastic clips that hold the markers in place. Unplug old marker, plug in new one and snap back into place. The brake and red marker lights should take about 15 - 20 minutes tops to install. Yes - it's that easy!!
The yellow marker lights are a little more difficult in that you actually have to lie on the ground. Unplug the bullet connector and loosen the 10mm nut off. With a little wiggling the marker will slide out. Cut the wire at the base of the old marker because you're going to reuse the female side of the bullet connector. Strip off a little insulation from the wire of the female connector and the wire of the new LED marker light. Use a butt connector to splice the 2 ends together.
This is the one I used:
Butt Connector
Reinstall the new LED yellow marker. Do this procedure 4 times and your done. As an aside - the first yellow marker on the driver's side has a ring terminal for the ground. Make sure you reattach it. The other 3 lights use the trailer as the ground.
Total installation time to replace an RT188 trailer with LED lights is under an hour.