Bought a set of tail lights of craigslist. They have 2 wires coming out instead of 1. SHould i just wire them both to the existing wiring?

Mine is a 1988 lights came from a 95

 

Can't really answer without more info.

There's a couple possibilities here.

If your existing lights have one wire that means it is the positive for the filament of the bulb and the light grounds through the body of the light to the frame.

A light with two wires could be:

1) The bulb is single filament, one wire is positive for the filament of the bulb and one is a ground

2) The bulb is dual filament, one wire is positive for the dim filament of the bulb and is the positive for the bright filament and the light grounds through the body of the light to the frame

Look at the bulb and see how many filaments it has. Or just try to connect the wires to your battery and see what happens. Try connecting one to the positive and one to the negative terminal, if it lights up you have scenario 1. If it doesn't it's probably scenario 2.

My Harleys all have three wire tail lights (blue = running light positive, violet = brake/signal positive, black = ground)

 

Thanks...

 

 

In 95 according to my FSM the tail lights were also tied into the brake lights. So that is the explanation for the 2 wires