The speedometer of my Series rig has never been honest with me about the one thing it is designed to be honest about. So I’ve been using GPS units from time to time. Genius that I was, I tore the headliner installing the first one. Bwana (my Land Rover) outlived that unit. Now I’ve repaired the headliner and discovered a better location. I removed the never used Citizens Band radio and affixed it there. Now I can see how sloppy the speedometer actually is. I don’t know if the problem is in the cable or the magnetic pickup in the gauge, but the GPS has solved the problem as far as I am concerned. This is necessary because having a behemoth Series III is like inviting speeding tickets, but only if there is a minimum speed posted.