poor ground will lead to higher resistance. Higher resistance can cause all sorts of problems, including sound quality and possibly the unit just plain not powering up. This is an S2000, don't half a$$ the job. Do it right the first time.

 

Also your ground wire can burn up. Friend's amp ground wire wasn't grounded correctly and the insulation around the wire burnt off.

 

I have it grounded to the car harness ground wire.

 

That's a good ground to use because its the oem. Some units may require a 2nd ground (e.g. in dash video)... I used a sheet metal screw and screwed it to the sheet metal under the knee pad of the passenger side.

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Yes high resistance = high heat as well, which can burn up insulation, but will usually cause the other problems first. Your friends problem might have also been in combination with too small of a gauge of wire for the ground.

 

I had assumed this was an additional ground wire to separately ground the case,
which would not normally carry current; however I just checked the Sony installation
instructions, and see that it is the only ground wire.
The easiest thing would be to splice it to the adapter harness' ground wire,
thus grounding it through car's harness to a factory ground point.

 

Thats What I eventually did... much easier