Here's the WebElectric unit I installed. It is very solid and sealed and installation instructions are simple and straight forward. Takes maybe 10 minutes. When you press the brake it flashes 5 times and then goes solid. I asked to have a unit without the "delay" feature that others may prefer.

 

how does it connect with 3 wires?

 

The car wiring has only two wires, of course; white which is hot and black which is the ground. The Pulser's blue wire is connected to the car's black wire with a plastic wire splice that is provided. The splicer has two "channels" one which you slip the black wire into and the other receives the unit's blue wire. You simply crimp the splicer with a pair of pliers and the wires are now connected without making any cuts. You cut the car's white wire and strip a half inch of insulation off each side. Then you attach the white wire from the Pulser to the white wire side you just cut closest to the tailight with a wire nut that is supplied. The Pulser's third wire, red, is wirenutted to the remaining half of the white wire which goes to the brake. You can see very clear instructions here. http://www.webelectricproducts.com/ Click on "online instructions". The Universal Model works for us. (BLP-1)