Need a little help??

This is a good excuse to go buy a cheap digital meter. Then you can figure it out for certain by using the ohms scale to figure out what wire is feeding the center conductor of the bulb - which will be Pos.
Otherwise, since black and white wires are mixed there's really no telling. If the wires going to the new light never touch frame or chassis ground, it doesn't matter what wire goes to each side of the bulb.