If you don't have a good electrickery circuit, which needs a clean feed from the switch and a good, clean return to the battery, then things don't work efficiently.
The reason fro taking the resistance of the wipers from the screen is so that we can isolate where the problem is.
The next stage it to check the condition of where the earth is connected to the body.
On mine the earth from the motor is a black wire with a ring connector, which shares a motor mounting bolt for the strap. It has been known to be a bit fiddly, but make sure that all the components are cleaned up before you put them back together.
Then come back and let us know how you've got on.
