http://www.volvowiringdiagrams.com/?dir=volvo/740%20Wiring%20Diagrams

Get the file "Volvo 740 1991 Wiring.pdf". The example may not include all options. You'll need to get an adapter to connect the after market stereo receiver line level out to the factory Volvo stereo with a remote switch or wire built in to a remote switch or the radio remote amp connection. You you can make one.

With adapters from places like crutchfield.com, you can connect aftermarket audio with the factory audio wire harness connectors. You can then remove unused equipment and wiring. Unless you've replaced the original not very powerful speakers in your 1991 740, most after market stereos should have enough oomph for a six speaker stereo. Though as each speaker is four ohms, you may want a unique amp for the third speaker pair. Does yours have those dash speakers with a midrange and tweeter (for imaging)? You may want an amp out for that, too, through a crossover. You may want to inspect and replace any two-decade-old dash speakers. You may find front dash speaker replacements from 850s with clear or black nylon or other durable drivers.

Questions?

Comments?

cheers,

dud.