The crawl report shows a lot of 404 errors

[shopwcs]

They are inactive products, and I can't find any active links to these product pages.  How can I tell where the crawler found the links?

[anthonydnelson]

That's too easy Keri.

[KeriMorgret]

If you download the CSV of the report, there is a column that will list the referring URL for the 404.

[josh-riley]

Mike's suggestion is a great one. SF gives some great data that's easy to play with in Excel. The free version only crawls 500 pages, so if you have a small site, you'll probably get what you need. (I got 30k+ pages, so I use the paid version that's only about $160/yr.)

[anthonydnelson]

There is nothing wrong with having a "404 error" if the page is an expired product. Obviously, you don't wont to be linking to a 404 page on your site, so I'd suggest using a tool like Screaming Frog, potentially even OSE, and monitoring your 404 pages in Google Webmaster Tools to see if it is still currently being linked to.

If the page has external links pointing to it, I'd recommend 301 redirecting it to whatever category/subcategory the product belongs to.

[Mike.Goracke]

Do a scan with Screaming Frog. It can point out exact pages where you are having broken links.

They have a free trial and a paid version.

This program is great for diagnosing many different website related issues.

Hope this helps.

Mike