radio terminal block

Hi All; Someone replaced the radio in my SC 1995 bus.The front speakers work but not the rear (The front speaker wires and power wires are plugged into what appears to be an original terminal block).I pulled the radio out and the rear speaker wires from the radio are not connected.Can anyone describe the terminal block for the rear speakers or ideally a photo.There are spare blocks but I am not game enough to start tapping into them to find out whats what.
Cheers