This is a taillight adapter which will convert your two wire system on your towing vehicle up to a three wire system to your towed vehicle. Certain applications will be say, your RV has a four wire system on it or maybe a five wire system converted down to a four wire but your towed vehicle has separate turns signals and brake lights. You would use this box to convert it back up to that at the rear of the vehicle. We'll cover a few technical points on how it actually gets installed. We'll show you how it typically gets installed, the nuts and bolts of it. It's a little bit easier than you think. Basically we're going to use this four pole wire harness as a model here, this is going to be the lead that's going up to the RV or towing vehicle. What happens is you have the four wires obviously, the ground, running lights, and turn signals.These are going to be inputs on this side of the box labeled input. Basically you're going to do it color for color if you notice you're going to have the brown wire left out. That doesn't have to be changed or anything that can go straight out to your taillights. Chances are you're probably going to have to split this to go to the left and right side taillights. To recap, this is going to be color to color on that and this will go up to your RV. On the opposite side here, where it's labeled output this actually gets connected to the wire harness itself on the towed vehicle. These will go right behind the taillights, so for instance on the left hand side your yellow will get connected to the left hand turn signal. The same thing for the green except it will go to the right. If you notice on the stop signal there's one wire, again you're going to, just like the running light, split this off to the left and right stop light signals. Other than that, it's a pretty simple install, it looks complicated but if you take it step by step, it's going to be pretty easy to do. As a final note, this is a heavy duty relay unit which may be mounted a...