MS on a 02 car?
 

how would it work, what cool function would i lose over the standard pnp since i'm guessing it will have to be ran as a piggy back.

what all would i need to buy and who can make a harness?

There is no plug-and-play Megasquirt for the NB.

But don't use it as a piggyback either. Install it as a parallel system.

Use an extension harness, such as Boomslang's, to connect the MS to your stock ECU. Then physically cut the wires that you won't need. The idea is for MS to control fuel, spark, and timing, while the stock ECU controls idle, A/C, and all non-engine stuff.

There are * some * people who use MS2 as a standalone but it's more of an experiment, or so I understand ....

The one real headache on these cars is VVT control, which would need the stock ECU. You can get pretty much any of the MSPNP features up and running in a parallel install with the right mods. The extra features of the MSPNP are more along the lines of having it delivered ready to plug in and go, as opposed to extra I/O.