Shtbox

Hey guys was about to go work this morning and truck died so I did a quick search and read about this issue with the ground for the coils that goes into the big harness.so i tried to probe it with my test light and got it to start then I started moving the big harness around and it cut out.Will it be ok to solder a dedicated wire to the main coil plug for ground or does that ground that goes into the bundle of wires also ground other wires?any body ever deal with this before?thanks in advance for any help or input