peugeot 106 car stereo

Try pulling yur speakers,not all the way out, but far enough to note the colors of the speaker wires plugged into them,unless your speakers are amped or the wires arent factory, the same colors at the head unit should be at the coinciding speaker. The ground should be black, acc orange, constant red, if those are your choices than thats what they are,if  not than im sorry im just a GM guy.

I don't know the wire colors either, but just use your multimeter and test them one by one.  Set your meter to voltage (12volts or more), then test for constant power (connect to yellow).  Next, turn the key on, and find the wire that shows power in the accessory positon (red).  Now set the meter to resistance, and touch one lead to ground (the cigarette lighter rim will work), and test the wires for a low resistance.  This will be your ground.  When you test these wires, turn your parking lights on/off to ensure you're not using a dimmer/illumination wire.  I don't think your car will have one, but I've never done one of those, so check just to be safe.  Now with the meter still set to resistance, test pairs of wires until you come up with a reading close to 4 ohms.  This will mean you've found your speakers.  If you take a small battery (I've even jumpered from the constant/ground in the harness), touch the wires to the battery posts (one wire to negative, the other to positive).  Hear that?  Make a note of which speaker it was.  It may be easy to have an assistant help you with the polarity.  If you "pop" a speaker with a battery, and the cone pushes out, towards you, the wire touching the positive post on the battery is positive.  The other will be negative.  If the cone pulls in, away from you, then you have the wires reversed.