Strange Speedometer Cable

During a "energy crunch' period there was a thingy that turned on a lamp at a certain speed ( 65 mph maybe ). Regardless what it is you can omit it with a new single piece speedo cable. Do the research, identify what you have before you order though. The size of the collector nut at trans end changed again somewhere around 75. Other late model owners have found incorrect application charts in aftermarket. Cable received wouldn't hook up.