Guys, I know this topic has been covered pretty much. I found a link the other day I was going to go back to and read but now I can't find it. Anyway I currently have a sony xav-w1 unit in my 2002 verada which was in it when I bought it. I was looking at updating to a more complete unit and was wondering. If I get an aftermarket unit perhaps off ebay do they generally connect straight in to our cars with the supplied iso harnesses etc or do you usually have to buy an extra bit such as a mitsubishi plug to adapt to the aftermarket unit.
OR since I already have an aftermarket unit installed does this mean that the plug in there could possibly be used to plug into the new unit. I haven't checked what connections are behind the unit yet, it only hit me last night that I have an aftermarket unit in the car now rather than the original mitsubishi unit.

What brand of aftermarket one do you already have?

All depends on how the current unit is installed. It may just be cut and shut, ie the original plug is cut off and the wires connected to the harness that comes with the radio. If that is the case, you will have to do the same.
You may find a radio to ISO harness and an ISO to car harness plug though. You would then need a radio to ISO harness to suit your new radio.

sounds messy. as stated above the unit that came with the car is the sony xplod xav-w1. as mentioned i have not looked yet so not sure how this unit has been installed. hopefully the correct way. I have a pdf of the install guide for my unit but am not allowed to attach things yet.

You would have to go for a same brand unit to have a chance that the plug will be interchangable, and even then it isnt guaranteed..

If you're lucky, the previous installer has spliced off the original wires, meaning the aftermarket plug can be cut off and the ISO plug will still be there.. which will mean you can either resplice the wires, or find a suitable adapter, from Aerpro or the likes.

Easier and cheaper than each of those options is to get some 'pin terminal connectors' that you crimp onto each wire of the new harness, and poke them into the female sockets of the old harness. Only problem I've had is getting the ones small enough to fit in the mitsubishi harness, last time I tried I ended have to cut and grind down the pins to fit... that was annoying.

That sounds way easier and cheaper than not buying an extra parts and just splicing the loom :S

haha chrimping pin terminals on and fitting them in the original plug just sounds like a waste of time plus you cant be assured they wont fall out ,the adaptors cost between 10 and 15 bucks only takes 5 -10 minutes to solder it together and is far more reliable

If the head unit was installed correctly and the original harness is still there, buy one mitsu ISO and one sony ISO, plug together, plug into the car and put the head unit back in and you're done. No soldering required. Also be aware of you're buying a head unit with features such as bluetooth or dvd there will be additional wires needing installation that won't be part of the standard plug.