In v10, you will need to activate related products by creating a new setting called RelatedProducts.NumberDisplayed:
Give the 'default store' (and any/all stores that you are running) values for the number of related products that should show up.
The related products feature gives store admins the ability to cross-sell or recommend additional products to their customers. There are 2 ways to set up related products: Pre-Determined, and Dynamic.
Pre-Determined Related Products
The first method allows store administrators to specify which products should be linked together.
Setup
First, list the IDs of the products you would like to be related (this must be done for each product) on the Options tab within the Manage Products page in the admin console. Use the Related Products Helper to find products by name.
Configure the RelatedProducts.NumberDisplayedSetting to determine the maximum number of related products that will display on product pages.
Display
Related products configured this way will display at the bottom of product detail pages:
Dynamic Related Products
The second method of configuring related products allows the software to pick which products are displayed dynamically. It does this by looking at which products customers viewed together in the past. For instance if a lot of customers who view a TV also view a special HD cable, the cable may appear as a related product for that TV.
Setup
Configure these Settings as desired for your site:
Setting Name
Description
RelatedProducts.NumberDisplayed
This controls how many dynamic related products to display.
DynamicRelatedProducts.Enabled
Setting this to Yes enables this feature.
Display
Related products configured this way will display at the bottom of product detail pages exactly as pre-determined related products do.