Just thought this mght be useful.
This is based on a 155 V6 1995 model.
The covers for the front speakers can be gently prised off using the slots provided. The actual speakers are also prised out. Prise at the yweeter end of the assembly as 2 spring clips hold the woofer end.
The cables can be easily identified as +ve and -ve by following the wires to the tweeter assembly. The terminals will be marked + or - accordingly. Snip off the yellow connector and solder on your new speaker wires with their terminals. Most are made up of one larger than the other. Just check that the +ve goes to the positive etc. A quick check if you have got speakers that don't actually tell you is to trial connect them by just twisting the wires together and then playing a bassy tune. The cones of the speaker shoudl throw out at the beginning of the bass note on each beat.
Note on sizes of speaker. The front holes will accept either a 10cm co-axial speaker or a set of 10cm components. If you use a co-axial speaker type, plaster duck tape over the hole the tweeter leaves in the dash. This will improve sound quality.
To place the front speakers in position thereare 2 choices. Either screww 4 holes through the dash, or use silicone sealant to ed them in place. The silicone acts like sound deadening and reduces vibration, however it ise pretty much permanent. The choice is yours.
When the speakers are all wired and connected, ensure they are snuggly in place and replace the grills.
Utter pain in the butt. To get the old ones out it is easiest to get into the boot! Yep, thats right. First unclip the boot lining 2 twist clips on both sides, 2 push fit holders and a nut. A good quality long shafted phillips head screwdriver gets the speakers out. They are tight, they are difficult to see and your back will hurt afterwards. The screws you need are the 4 inner ones. The outer 4 hold the grille in place. (See Note below!) Oh yeah, remember that when the last screw comes out the speakers fall down, on your head if it is there.
Note on speaker selection. The speakers to go in the stock locations need to be very flat faced. If you buy co-axial or tri-axial speakers, lay them on a table, cone down, if they rock by more than about 3mm they won't fit. The speaker grill is so near the speaker face that you won't get more than 2 screws in place at all.
Wiring the back speakers: The Alfa back speakers don't have terminal labels, however, on the left the +ve is the solid colour and the negative is the one with the strip, and on the right the -ve is the solid colour and the +ve is the striped. (I don't know if this is an Alfa screw up, or a problem in my cars past.)
However you can again easily check by connecting them and playing a bass tune. If they throw outwards on the beat they are connected right, if they throw inwards on the beat they are the wrong way round.
Check your polarities and solder all your connections, now remember to insulate properly using shrink tubing or proper electrical tape, don't use cheap trash as it dried up and unwinds.
When all is in place, run the stereo. Use the fader and balance to listen to each speaker on its own, then the back together, then thefronts together. If 1 speaker is out of phase, ie connected the wrong way round you will hear a kind of wow-wow-wow sound on the bass tune. Again the fader and balance controls help, when one speaker is off and the others sound fine you have found your culprit.
Other Notes: Screws, you will lose at least one down the back of the steel work in the boot, the car will just eat it and it will never be found. You will find that just after you have put all the speakers on, you have left a screwdriver in the dash or in the boot metalwork.
Good luck, and remember, I ain't no sparky. Just don't run your stereo when two speakerwire of different polarities are touching, the headunit will not like it, at best you will blow a fuse, at worst the whole stereo. Happy changing.
I used Kicker EX42 10cm co-axials in the front (£39.99 from Halfords) and 16.5cm Pioneer tri-axials in the back (£59.99 from ICE-direct in Peterborough) The head unit is a Blaupunkt MP72 Los Angeles(£219.99 from www.bluespot.co.uk),
and with no additional amplification the car is now louder, and more importantly clearer.