Re: 740 GL 1989. I am trying to install an upgrade JVC radio/CD player in place of the factory radio/cassette. I have a Haynes manual that covers up to 1988 only. Unfortunately, the most recent diagram in that manual shows a completely different radio...it does not correspond at all to the wiring that I actually have. I have identified the non-switched power, power switched by the ign key, and ground. Also, there is a white wire and yel/white which has abt 5 ohms across it, which goes apparently to the RH front speaker. This leaves two wires, that I assumed go to the LH speakers...but they do not. Don't have a clue what those two are.
There is another plug on the original radio, a round one with abt 6 small shielded wires, probably for speakers (what else?) but I checked for continuity from any of these wires to either of the front speakers, and there was none.
The only way I can complete the installation is to physically trace the wires from the four speakers back inside the dash and see where they terminate. THis would take days! So I am hoping someone can supply the info for this particular radio installation. Thanks, Jim