Amendment to my question, I have realised that it will search by sku, but my issue is a little more complex. Most of my products are setup as grouped products.
i.e. I have 2 variations of a product which are setup as separate products which are hidden. There is a grouped product also setup which is the one shown to the customer with the 2 hidden products associated to it.
see https://www.stitchtastic.com/store/harley-davidson-circ-1933-cross-stitch as an example.
the grouped product has an sku of KAS-0470-GRP which works,but I also need it to work with skus of KAS-0470 and KAS-0470-K
In the Instant search plugin administration, there is a setting called "Visible Individually Only", could you please uncheck it and see if there are any difference?
Looking forward to your reply!