What is the function of this silver unit (letter C) by the fuse box and

Almost looks like the starter relay best I can tell. I'm sure someone that knows more than I will chime in, but that gives you a theory to start researching. It's been far too long since I've had an abode for me to be able to say which wire goes where. However, if I'm not mistaken (IF) a and b go to the ballast resistor.
Sorry I can't be more help bud.
it's under the dash, not hood:D