I got hold of a speedo problem I have never seen before. With the ignition on the odometer will read 499.E. The speedo will be at 0mph until you move the bike forward, then the speedo jumps to 70 to 80 mph. This happens engine running or not. I have pulled the speed sensor and cleaned it to no avail. I have ridden the bike and the turn signals cancel properly. The bike is a 1996 Sportster 1200. I've allways been pretty good with electrics, but this one has me bugged. Any help would be appreciated.