Just installed an Alpine CD-AM-FM unit in my wife's 90 745T. This car had the standard factory radio and small amp.

Unlike my previous installation, in an 88 740, the amp and radio plugs are both the large rectangular AMP connectors. My radio had a nice harness made up to a 9-pin old style radio connector. I wanted to do the install in such a way that the original stereo could be plugged back in if needed, if the car was sold for instance. Every so often my "keeper" cars get replaced when something better comes along, so I wanted it to be a neat installation.

I'm usually against using the "tap-in" type electrical terminals, but in this case, they would be the best and easiest method. I also needed to add lengths of wire to the speaker connections to extend them from the rather short stereo harness to the amplifier plug- none of the speakers in this car are powered directly from the stereo, but rather all 4 are powered from the little amp over by the steering column.

I found out after the fact that there are now available some correct plugs for interfacing to the big AMP connectors- though they're not cheap. Crutchfield and Installer.com sell these plugs, and they get 15-20 bucks for them, plus another 15-20 for the faceplates. Not as cheap as they once were, though they do solve a tough problem for a lot of people.

However, even with these plugs you'll be making quite a number of inline splices and adding wire for all the speaker connections. No stereo I've ever seen has the 3-feet of wire needed to reach comfortably over to the plug for the amp.

Here's what I determined for wire colors, something that doesn't seem to be easy to find:

1990 VOLVO 740T/ 740GL Stereo Wiring

Color codes for factory 4-channel stereo and remote amplifier:

These wires all terminate at the large 14-pin AMP rectangular connectors. The small round DIN style connector, for stereo outputs (inputs to amp) will not be used in any aftermarket stereo installation.

Crutchfield, and others, sell adapter plugs for these connectors, for $20 per kit.
http://www.crutchfield.com/S-QloRQSmY1ZJ/cgi-bin/prodview.asp?g=103000&I=120701121
Installer.com gets a bit less for the same kit:
http://www.installer.com/item/display_item.php?it=70-1120

Stereo connector:

Black: Ground
Green/Red stripe: Constant power (battery +12V)
Orange: Switched power (ignition +12V)
Green/White stripe: Power antenna (12V applied raises antenna)
Yellow/White stripe: Dash lights
White: Dash lights (connect to Yellow/White to energize light relay)

Amplifier Connector:

Black: Ground (2 wires)
Pink/ Black stripe: Constant power (battery +12V)
Grey & Grey/White stripe: RF speaker
Blue/Yellow stripe & White: LF speaker
Green & Green/Brown stripe: RR speaker
Yellow/Grey stripe & Yellow/Brown stripe: LR speaker

I have this as a Word document; if anyone would like me to forward it to them, just email me at: myvwsgotme (at) snet (dot) net.

Hope this helps with your installation!

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::: Rob Bareiss, New London CT ::: 92 244 M47 212K ::: 90 745GL M47 275K ::: 90 745T AW71 213K ::: 90 745T Parts Car ::: 88 245DL SOLD! ::: 84 242DL Project ::: 70 VW Bus ::: 70 VW Pickup Project ::: 71 VW Notchback :::