You can do it 2 ways, cut up the old stock loom, or run new wires if you want a bigger power wire or anything. I'll tell you how to run new wires.
Look at the loom for your new deck, if it has inline fuses on the wires already (if you dont know what that is they will be like black litttle boxes on the wire) you're job just got a bit easier. If it doesnt, heres your shopping list -
Red wire with a fuse for Acc. (the guy at the audio shop will know what you're on about.)
Yellow wire with a fuse for constant power (again, the guy will know what you're talking about)
Black wire without a fuse.
Speaker wire.
Measure how much you need and add a meter in case you stuff up.
Solder/soldering iron/heat shrink/crimps OR just crimps OR electrical tape (bad idea).
DISCONNECT NEGATIVE BATTERY TERMINAL NOW!!!!!!
Ok grab your yellow wire and feed it through a grommet in the firewall, choose a safe path for it to get down to your POSITIVE battery terminal.
Solder a crimp with a loop on the end so that you can put it through a bolt in your battery terminal...and put it through the bolt in your battery terminal. TAPE OFF THE BARE END OF THE YELLOW WIRE THATS INSIDE THE CABIN. (make sure the fuse is fairly close to the battery)
Take off your steering column and ignition barrol surround by undoing the few screws from underneath. Go re-connect your negative battery terminal and grab your circuit tester, put the ignition to Acc. and start poking metal connectors untill the tester lights up, may take you a few terminals to find one, make sure it turns off when you put the ignition to "off". In other words, find a terminal that only works when the ignition is turned to Acc. Solder the end of your red wire into the wire coming off the terminal and use heat shrink or tape to insulate the join.
TAKE OFF THE NEGATIVE BATTERY LEAD AGAIN!
Find a metal body in the car, if you can find a bolt or screw that goes to the body of the car that is good. solder or crimp another one of those loop crimps onto the end of it and screw it down to the body of the car. easy enough.
easy enough, put speaker wires on the speaker connectors.
Now join the wires, yellow goes to yellow on the deck, black goes to black, red to red etc...
Your manufacturer will tell you which speaker goes where.
Pioneer:
White: left front.
grey: right front.
purple: right rear.
green:left rear.
If you plan on running an amp, run a blue wire from the remote wire on your deck to wherever your putting the amp, same goes for a pair of RCA's (one pair of RCA's per amp, but some amps can daisy-chain so it depends on your amp) Theres other wires for automatic aerials and phone kits but who cares about them.
Now sit your deck in there and drop the battery back into the circuit dont tighten it up yet, check if anything starts smoking, if it does, pull the negative lead off again and go see what you stuffed up. If nothing starts burning, tighten it up. Go see if your deck turned on, if it doesnt, again go figure out what you did wrong (circuit tester is your friend).if it does turn on mount it properly put everything back together put the beauty board over the front of your amp and crank the phat beats yuleh.
Pretty sure its all good, correct me if im wrong I probably forgot something...
Run new wires...chopping and taping random wires and s*#t like that is stupid. The loom in my car is chopped and taped everywhere...annoys the s*#t outta me.
but what i want to know is what does the colours mean e.g what colours is is power ect would love if some one could tell me what they all mean