see the yellow wire with green stripe. thats the one. i have not spent any time on this job, just got a long wire , added a thimble and ziptied it, because it was an experiment, now i will make a proper grounding kit from audio grade wire.
for your wipers, first clean the thimble for their ground. if it still doesn't improve, the problem is most probably with the switch (stick).
as for what the electrician did, i would use audio power wire to make a ditto copy of the original wire and replace it. or atleast add a fuse