Just recently bought an australian spec 318is (E30),

After trying to rewire the less than conventional standard BMW stereo, I experienced some wierd problems electrically. Bare in mind I have only touched/cut the wires related towards the stereo. In the middle of doing this the speedo stopped working altogether.

I needed the car part of the way through finishing the job, so I drove it without the radio connected, but in this time the centre console light (not sure if this is aftermarket) started flashing and beeping, not loud but just like a notification beep and a completely random tempo. I was told the alarm system wasn't activated by the previous owner, i think i might have changed that somehow. Disconnecting the battery had mixed results and i don't have a remote. Now i can't start the engine, starter motor turns over but no ignition, how do I properly uninstall the whole system without causing damage?

Alarm system is a Cobra (very old model i'm told) with immobiliser and panel sensors.

Any ideas to whats caused one or both of these problems?
Thanks