How old is the battery? That is a very significant drop in voltage. I would have the battery tested. If the battery tests good, I would assume its a wiring/corrosion issue. If you want to do some proper testing read this. http://www.northernmobile.com/vdrop_two_page_handout.pdf This is a generic han...

WAI may possibly be listed under WPS depending on the distributor. Here is the one you need for your 850.
https://www.rockauto.com/en/parts/wps+/ ... rator,2412

You have the 140A alternator with the clutch pulley. I work at a starter/alternator rebuilder, but we can't ship to Canada. Try a local auto parts shop. Here are some part numbers that will work. I know the WAI unit is available on amazon for $147 US https://www.amazon.com/Discount-Starter-Alternato...