black wires off coil

hi hope all well,
daughters car is 1.8 gti cabby 1990 with electronic ign and picked up just over a year ago with mess of wiring but worked.. really well...off road over winter but now currently have no spark although it has fired on literally 1 cylinder once.
checked leads and coil with meter but just in case swapped with spares..hall sender seems ok..tacho has never worked but that was in the list to do...
so trying to find out where 2 black wires from coil (primary?) go to, as one seems to occasionally earth (meter) (literally continuity then nothing,)  believe 1 goes to fuseboard not sure about the other.. age is becoming a big old number so any help welcomed, thanks

 

Just to say all done..nothing obvious so maybe an earth. Thanks

Black wires are not grounds.  Brown are grounds.