2003 lightning.....correct? a problematic ACC blade fuse not related whatsoever to grounds. below is list of what is fed on your model by the ACC fuse. i am assuming a fuse of proper amp rating OR no more than 10% greater strength in use here.
ACC fuse feeds: TAIL LIGHT, LICENSE PLATE LIGHT, HEADLIGHT ASSEMBLY, TURN SIGNAL FLASHER.
you need to do this: unplug the tail light/license plate plug which is near your battery box..... unplug the flasher....you already have headlight connector unplugged BUT this does NOT eliminate it as the source problem.
now replace the ACC fuse. what is the result? see below:
if the fuse is now ok it is your flasher. if the fuse now pops again it is the wiring loom at the steering head.
keep in mind that each of your factory turn signals IF still installed on the bike have the positive feed wire running thru the center of the metal inner post. it is rare BUT that feed wire can rub thru striking metal. if you find from the above steps i've provided that your flasher is the culprit CAREFULLY CHECK each turn signal assembly wire for this happening prior to replacing the flasher or it will happen again.