I had sudden loss of my instrument and other associated dash lights without any prior manipulation of the electrical system. The exterior lights on the same fuse circuit(21) remain operable. I felt it might be the instrument rheostat and removed it. My manual doesn't explain its electronics or wiring, but assuming red as battery, blue as lights, and black as ground, I was unable to demonstrate continuity between red and blue with the rheostat in either position. Is this the proper test for the rheostat?