It can be tight there.
I don't know how much it helped but an old trick I used was placing a short section of fuel hole over the sprak plug wire nearest the wiper motor. Maybe four inches long and cut lengthtwise so it could be be slipped over the wire.
I do not know enough about the relationship between electrical noise and electromagnetic interference to suggest quick ways to tell them apart.
I assume the first would show up on an oscilliscope.
Both
@KitCarlson and
@halifaxhops may have some perspectives on this.
