if you know which wires are positive and negative on the radio, try this. place the speaker on a bench. connect one terminal of the speaker to the negative post on a 9v transister battery. then momentarily connect the other terminal to the positive post on the battery, and watch the motion of the speaker cone. if the cone moves outward as you make the connection, the positive post is connected to the positive terminal of the speaker, and you can mark it positive. if the speaker moves inward, then the positive post is connected to the negative terminal on the speaker, and it can be marked negative. hope this helps.
