Hi Michael,

Personally, I think you already pretty much know everything you need to know. All you need to do to install the decoder is:
1. Remove all wiring except for the black wire with the "Drossel" (usually grey coil-like part) in it, you can simply hook up the black decoder wire to this coil and leave the other end of the coil in place, i.e. at the motor cover.
2. Remove the direction switching relay
3. Hook up the red decoder wire to the pickup slider (by unscrewing it, you'll notice a small copper plate on which the original wire is/was soldered, you can solder the red wire on that position. (Take care it does not short anything, so don't remove too much of the wire insolation and "tin plate" the wire before installing it.)
4. Connect the brown wire to the ground, usually this is done easiest by attaching it to the little copper lip connected to one of the screws that hold the motorcover in place.
5. Connect the grey wire to the front light, and the yellow one to the back light.
6. If the light armatures are not connected directly to the ground, ground the bulbs by using the orange wire. This will probably not be the case, as the 3088 also is not equipped with Telex couplers, remove the orange wire by cutting close to the decoder and insulate the remains properly. The same can be done with the white wire, as not extra functions like Telex are present on your model.
7. Finally: solder the blue and green wires to the motor coil.
8. Test the model, if it runs opposite to it's light switching, swap the green and blue wire.
9. If you don't feel completely confident at first: don't shorten any wires, go through steps 1 until 8, if all works properly, loosen the wires again to shorten them to the correct length one by one.

Maybe this link is of use to you: http://www.bogobit.de/decoder/66032.html

Good luck!

BTW, the last two Märklin Magazines deal with this exact issue. The first goes through the solder bridges in order to get functions from the 66032, and the second article goes through the conversion of a simple Lok like the one I plan to do first. Thus, I thank all for the help, and feel confident that I will be OK.--MM