I recall a topic back 2-3 years ago where wiring these guys (like below) was discussed. I tried searching for it and came up dry. On ebay they come in 1, 2, 4, 6, and 8 relay versions. I bought a couple of the 8 relay versions back then, but they came with zero documentation. I found a document online that had a fair bit of info, the most useful of which is right at the end called Pin Wiring.
I tested one of them out the other day to see if I could make sense of it. Once I found out how it actually worked I edited the pin wiring section. Copy attached for anyone who can make use of it. But I have a question. The two methods of wiring seem to be 1) direct to the coil from the inputs, or 2) indirectly through the built in opto's, so the inputs are isolated from the coils. In both cases however it seems you need to ground the input to activate the relay. I could not find a way to trigger the relay with a positive input. Has anyone found a way to do this??