wiring aftermarket tachomete

[banpei]

It should be perfectly possible as long as you have a tacho that is suitable for a four cylinder car.
You can look up which wire to pick up from the combination meter in the wiring diagram manuals (EU or USDM) or the body repair manual (page BE-22):
http://www.aeu86.org/technical/ae86-manuals/

Or you draw a new line from the coil directly and fuse it properly. I think last month's edition of Practical Classics had a nice how-to on the whole subject. I'll have a look if I can scan that article.