Wireing for added tailights

Does your rv have red lights for brake and running lights and amber lights for turn signals? If so and there is no converter box it is probably wired incorrectly.

Import vehicles with amber turn signals use one wire for each turn signal and one wire to power both brake lights. If there are only 4 wires connected then it is probably wired for the two turn signals the running lights and ground with no brake lights. If this is true you would need something like this.
Link

As you can see in the photo, the converter takes the separate turn signal and brake wires and combines them into two wires that power both the turn signal and brake on each wire.