New speakers and speaker wires, so the fader is no longer an issue.

You're trying to connect the following to the new HU to get functions:

1) Switched power so the radio turns off with the ignition
2) Steady power so the radio doesn't lose presets
3) Ground
4) Accessory signal for antenna and amps
5) Maybe - a variable voltage to adjust intensity on the lights w/ instrument lights

This thread has some info on the 240D. It's important to remember the 240D was more basic and may not have the same OE wiring harness as a 300D/CD/TD. Specifically the 240D may not have the requisite steady +12v for those "deluxe" solid state radios. http://www.peachparts.com/shopforum/showthread.php?t=298631&highlight=radio


You can buy adapters or eyes that will let you tap directly off the battery. For your trunk mounted amp off the marine cable, get one of those and install an inline fuse near the battery in the engine bay.

For the amp "remote", yes, you can splice the antenna "trigger" wire and the amp "remote" wire to the blue wire from the HU. The antenna does not draw power for the motor from this wire so you won't be drawing too much current. For the 240D with the power antenna the wire should be Blue/Red or maybe black or maybe blue.

More info here: http://www.peachparts.com/shopforum/showthread.php?t=299281&highlight=radio

Matching these up with the above list:

1) thickish red wire from the harness for ignition switched +12v
2) probably better off your battery tap - but maybe off the dome light
3) the brown wire for ground -- but if you've already got a good ground elsewhere on the new harness you don't NEED to use this wire.
4) blue/red between radio and antenna switch for +12 when radio on
5) maybe the grey/violet wire going to the lights, if you're adventurous

Get a multimeter, use the continuity and voltage functions, check wires in different settings (e.g. ignition on/off, lights on/off). Check fuses before you start and read up on a few other installs. I think fuses 1, 2, 4 and maybe one other one can affect the W123 install on the 300D, maybe on the 240D, too.