Add a radio harness to OEM wiring? Reasons NOT to?

[phenryiv1]

I purchased my e30 without a radio but the PO had installed some radio in the vehicle. The harness connector that is in the car is NOT the original one. Is it wrong to go to a JY and to purchase the car-side harness out of a common vehicle and to wire it up so that an off-the-shelf wiring harness (matching the donor vehicle) can be used to install the HU?

I will be installing a Pioneer HU and will be running an outboard amp so all that I really need are the 12V positive/negatice, 12V switched, and illumination wires. Everything else will be handled via the amp using the HU turn-on signal and RCAs that will supply the amp, then the OEM wiring (diverted to the aftermarket amp from the OEM amp connector).

I don't know what the PO did to the car so I intend to use only the minimum OEM connections. Should I add my own connector to handle the 12V +/-/stitched/illum or just run those 4 wires to the Pioneer input harness?

[StereoInstaller1]

There is no such thing as a "harness" for the E30, its individual plugs... So just use butt connectors

[august125]

If you plan to go that route I would pick up a standard ISO 10487 harness out of a Mercedes, VW, or Audi. You could also use a BMW Quadlock harness if you wish.