Hey. I posted similar post. "XJR Starting to Annoy Me." Another member left very useful feedback on my post since I am having similar problems. My wiper is all out of wack on my 96 XJR though. Doesnt matter whether you pull back on stick once or put it to low or high speeds. The wiper just keeps going and going for about 45 seconds then stops wherever it wants on the windshield!! Right now it is stopped on lower passenger side. I dont drive it in the rain but it's very irritating. Didn't do that when I bought it 5 months ago.

Hoping it's just the RELAY in right front engine bay location as other member advised in my previous post. Maybe you have same problem but your relay is completely shot versus mine acting screwy.