Depends on how far you want to go with the install. E30's use a booster amp off the head unit, but the stock head units put out a hi-level signal, so you can't put line-level into the booster amp and expect it to work (ie, a new head unit can't be one that only uses a separate amplifier). If you're shooting for optimal sound, then an install can get pretty involved, E30 radio setups are odd because they don't use isolated grounds throughout. The head unit, for instance, has single-wire-outs for both channels, which run through the separate fader in the dash, out of which goes 4 leads to the booster amp, and a single ground wire to the booster amp. Anyway, if you don't mind living with the sound quality more-or-less being what it has been, it's not terribly involved to tap into the stock radio wiring harness; it's just funky, because you have to wire all 4 ground leads for each out channel of your new head unit to the one ground lead going aft. As I recall, I think one lead powers on the booster amp AND the power antenna, and another lead dims the stock head unit display in sync with the stock dash/instrument console light dimmer. I believe there is a place in Florida that might be able to repair the stock head unit, but you could probably have a reasonably nicely featured newer head unit for the same or less $$$, and installing it's not that big a deal if you're willing to tap into the existing harness. Ideally, wiring connections should be soldered; stock head units I think have a bolt or pin or something that supports them at the back, a replacement unit won't have that unless you rig it up somehow- so a solid install of the mounting bracket is in order to hold it in place as well as possible - sloppiness leads to floppiness which leads to cd-skipping. Although many head units these days have USB connections, I don't know why they don't have hi-capacity-capable SD card slots... it's still a little pricey, but with a 128GB SD card available, that's more capacity than all but the largest IPOD classic and sure beats shuffling CD's... oh well! A stereo installer would likely cut all the stock connectors off - if you think you have any need for that in the future, you'll want to keep those plugs and connectors, you'd only get them from another scrapped radio wiring harness. The stock wiring insulation can be cut so you can solder connections, a little tricky to do, particularly if you haven't spent the last 20 years as a professional solderer. Wiretaps are easy, but not foolproof (that said, I've never had a problem, but...), particularly for power and ground - risks of shorts or grounds and some sort of power-short wiring meltdown are preferable to avoid. Optimal sound is another thing altogether. Running speaker wire to all speakers means pulling just about the whole interior out of the car if you're going to do it right, and even at that, the front door tweeters, besides snaking wiring through the door harness, take their ground off the chassis, so you have to rewire the speaker too, or replace it with something better that fits. Even if you might hope to improve your sound quality with a better head unit, you won't get too far with that unless you replace the stock speakers, which are ok, but definitely not 'wow mama!'. Having ipod accessibility might be a prime consideration for upgrading. E30's have been around for ages - search stereo topics here and elsewhere, you should find some useful info. Stock E30 head units have two 5-sided (vs hex) fittings behind two little doors on the left and right sides that you use something small and flat to flip open, and then a special 5-sided radio-removal tool that looks just like a small hex-nut driver to turn the pentagonal nuts. Although a hex driver can be jammed in and made to work, the radio removal tool is cheap, and keeps the locking mechanism functional - available from Bavauto.com and lots of other places. Since the system has both the head-unit and the booster amp, you'd want to verify what's dead is the head unit and not the booster amp - if the booster amp is dead and you don't want to ID/trace and bypass a bunch of somewhat inconveniently-placed wiring, you'd have to dig one up, probably pretty easily found on ebay.
