A couple things to help you along:
- the map light rear view mirror from the 325is is popular to put in. If you get the whole harness it is plug and play with zero splicing which is nice.
- the power sunroof is a full on conversion that has nor needs to have anything to do with the check panel. In entails the whole overhead console, the tubes for the sunroof cables, and of course the motor and relay with the bracket, in order to be done. This is a killer swap to do IMO.
I've done both of these conversions and they are pretty cool and very nice to have if you are a luxury and gadget nut like me.
Now for the check panel in particular. This 318is is my 4th E30 with the last 3 being 325is' that all had all of this stuff out of the box.
The 318is does not. So in terms of retrofitting, why you wouldn't want to is b/c you'd have to run wiring to:
- tail lights
- license plate lights
- head lights
- oil level sender
- washer fluid tank
- and a few other places
There might be a central set of repositories in the harness that you could splice into, but I'm fairly certain this is the one option that is not plug and play.
So what to do with the space? I saw someone who found that a Chevy truck's lamps went in there perfect and he modified the check panel. I am debating find a GPS that will fit up there and trying to go for an OEMish look. I've seen boost gauges up there for guys running turbos. Pick your poison.