Check your connections. in case you did not know (sorry if you did) the wiper motor has 12V from the ignition switch (via a fuse) on it permanantly, & the wiper switch supplies the earth connection. If a previous owner has wired the switch to provide 12V then that could be the reason you get lots of current, as the motor self park mechanism may be shorting it out.
Bob
Green is 12V from the ignition switch (via a fuse), so anything which only comes on when ignition is on will have a green wire going to it. The heater is one such item, so I am sure your diagnosis is correct.
But why was it disconnected??
Hi Miles. Your inbox appears to be full, I wished to send you a message regarding Shepton Mallet, & if you were going. Perhaps you could clear it, & send me a PM, so we can "talk"