Datatool Rev Light

[Mr.Mash]

Iv fitted one of theses rev lights but the led's are erratic the datatool website say's

"This is normally because the pulse wire selected is getting secondary signals from another source. For example if the tacho wire is also linked directly to another device (e.g. coil, fuel pump, etc), the secondary device often creates it’s own signals."

But does anyone know can i run a wire from as it say's either the coil or fule pump with out messing anything up?