75 came with either a mono or stereo radio. If there is only one of the "convectors" then it's mono.

A mono radio has three wires going to one convector while the stereo radio has six wires going to two convectors. The convector wires are Yellow-Blue-Green. Both radios have a three wire bundle for speakers...black for speaker grounds and a light green for the right speaker and dark green for the left speaker. There is also another three wire bundle: gray ties in with your parking lights to light the radio dial when you turn on your lights, black goes to chassis ground, and yellow goes to fuse box for +12V power.

Convector wires are green, yellow, and blue. If the connectors are cut off it will be impossible for you to tell the difference between a green speaker wire or the green convector wire. Turn the radio upside down and remove the bottom. The green wire to the convector connects to a terminal strip at the very furthest connection point (closest to the top of the radio). Or bottom connection as you are looking at it upside down. The green speaker wires are on separate terminals closest to the bottom of the radio.

The speaker wires are black (common to both speakers) and 2 greens. It really doesn't matter which green goes to which speaker as it is a MONO radio.

Use only 10 ohm speakers or you will cause severe damage to the radio. Most modern radios use 4 ohm speakers, so be careful.