I have a Link Trainer instrument

More precisely, an Tachometer. If i touch its two contacts, marked plus and minus, to a battery, I can make the needle move.I don't know if the RPM needle position is simply a function of applied voltage or if AC current needs to flow.Any ideas how I can get this to work via the PC and MSFS? I have zero electronics experience but I can definitely write a program to extract the variable from MSFS and apply it to whatever interface I can use, if I get motivated enough.More details: the instrument is from the 1950s and I bought it off Ebay for 47 including shipping :)