Uninformative and Unidentified

The rudder angle indicator on Silver Otter isn't working, and I'd quite like to fix that.  The first task is to get a meter on it and see if it's the instrument or the sender that's the problem.  It would help if I had some technical details so I know what I'm looking at but I don't recognise the brand logo - so I've asked on a couple of forums to see if anyone can help.