'64 Studebaker Champ-tail lights

[RSykes]

This truck is equipped with Signal Stat 4300 tail lights--a red wire and a black. Which is ground? Does it matter? The tail light lights up with wires placed battery ground/positive both ways.

[Skip Lackie]

I am not at home and can't check my parts book, so I assuming from your description of only two wires that the signal lights are separate lamps. If that is true, then it doesn't make any difference -- though the normal standard is that black is ground and red is hot. If the lamp has three wires, then it contains both tail and signal bulbs/filaments, and then black has to be ground.

[RSykes]

There is a single T1157 bulb.

[Skip Lackie]

If there's an 1157 bulb, then there are two filaments, and the lamp socket provides the ground. Ground the bulb body itself. Apply 12v to each wire in turn. The brighter filament will be the signal. The other one will be the connection for the tail lamp.

[StudeRich]

What is going on with the Tail Lights IN the Body? Or are you saying these are them?

[1954khardtop]

One wire is for the stop - turn light, one wire is for the tail light. The ground is thru the housing of the light. Usually the red one is the stop - turn filament, and the black one is the tail light. Try them with the wires twisted together, and you can reverse them if need be. When you have them correct you can solder or crimp them for good.
Edit, I see Skip in post 4 already said the same thing.