Hey guys, back again!
I was just curious if anyone had a wiring diagram for a 1990 740 turbo wagon. I'll be removing the stereo and installing an aftermarket stereo this monday! It's a very basic aftermarket dual cassette deck that just needs 12v, ground, and speakers. I won't be using the remote or preamp wires.
Also does anyone have any tips for speaker replacement? I'll be drilling out those rivets tomorrow but I don't want to mess anything up!

 

for mounting door speakers, I highly recommend the adapters from
PVC Speaker Adapters - CNC Machined - In Stock or Custom Made
which will allow you to use a standard 5.25" speaker.

you can get a harness connector adapter from various places which plugs into the factory harness. if your car has a amplifier over to the left of the steering column, you need one sort of harness, if it doesn't, you need another. you take these harness adapters and splice them onto the wires from your aftermarket stereo, then it all just plugs in. the harness for the amplifier has a 2nd connector on longer wires that you plug in where the amp used to be, to get to the speaker wires.


my 92 740 came with that amp, and small dash speakers plus rear door speakers but had no front door speakers. I used some component 2-way speakers with external crossovers, I installed the crossovers over where the amp used to be, I took the dead factory tweeters completely apart, removed the cone and magnet assemblies (destructively), and glued the component tweeters in place of the factory cone, then reassembled the grill, and put the component woofer in the front doors. this has a little too much bass -> treble separation, I probably should have just used coax speakers in the doors and left the dash speakers dead and disconnected.

even tho my car didn't come with front door speakers, the wiring was in the doors for them and was wired to the amp harness connector.