I found the answer myself using a multimeter. Looking down on the back of the 2000 TRAFFIC radio/cassette, when facing the front of it, the left hand connector is for all the speaker connections. The top four wires are for speakers on the left, and the four bottom ones for speakers on the right. Speakers on the same side of the vehicle sound best when connected in series, not in parallel. Counting down from the top, pins 2 and 3 were already connected together, as were 6 and 7. Speakers on the same side of the vehicle were connected in series first and then two links made to the output of the 2000 Traffic radio cassette. The active pins on this version were the top two (left speaker) and 5 and 6 (right speaker). The inactive pins were 4 and 8 counting from the top. By deduction they correspond with the output for the rear speakers when using the 4000RDS model.
JC; I raised the initial query before solving it., May 2010