A lot of disco's suffer failure of the spider unit. It is a junction box in the alarm imobiliser system. Its not hard to fix, just means taking out the middle section of dash ( radio, cup holders etc)
I did mine last year but just soldered up the dry joints in the unit.
Do a search on this forum for spider unit, there is lots of info. If you get stuck, let me know, and I'll forward you some step by step instructions that I followed with no difficulty.
Cheers
Andy​