Solonoids and optos will have nothing in common. If the Optical LED is bad, or there is a break in the connection going back to the 16 opto board then you should read around 12V on the LED, 10V seems a little low and may point to an issue with the 16opto board connections or possibly the filter cap; you will want to do a visual inspection of the large capacitor and check for swelling or signs of leaking.