In principle the problem is simple, but as Stevez points out, the coil/contact breaker connection is not a friendly place for electronics.
However you said:
novicepaul said:
the tacho is for 4,6,3 cylinder cars and I have an 8 cylinder car. :roll:
Two things get me thinking here,
the order 4,6,3, I think most people would write 3,4,6 or 4,6,8, not 4,6,3.
and
the fact that I can't think of one car with a 3 cylinder engine, but lots with 8 cylinders, (even some with 5, but not 3).
Could it be that the 3 is a badly printed/scratched/damaged 8 ???
If so, end of problem.
Try it and see, it won't break it.
JimB
Edit: I just did a quick search on Google, and found that some Daihatsu cars have a 3 cyl engine.