Haynes schematics are almost useless, you want factory schematics for your car.

You can try search engines: Google, Startpage, Duckduckgo, Qwant, Bing, etc.

More and more the search engines deliver paid advertisers wanting $34.95
for stuff thats out there for free.
How many search engines aren't the Google mob?

I just had disappointing results from Searching for specific manuals: lately the search engines have amnesia about the free stuff unless you are lucky and have the correct search string. (I suppose this is to protect them from antitrust actions)

You can goto www.startpage.com and search this string:

"volvo 850 wiring diagrams"

Then you start to home in on usefull info.

This is from startpage:

Goto: https://www.yumpu.com/en/document/view/29679775/volvo-850-1997-wiring-diagrams

Try various search engines and compare results, let me know if you find
a better search engine. They tend to disappoint with the monopoly in place.

BB