The 83 Aspencade had a digital speedo with a box at the wheel converting the drive to.electric pulses. The 1500s all have manual drive cable to the back of the speedo
The 99 screws on the wheel the same way with the Phillips screw, both use the same style drive box on the wheel /axle, you just have a cable now all the way.up and it has to unscrew at the top, you get to it from the left under the handlebars, through the tunnel, remove left tunnel plastic insert piece, it's tight and blind working area done by feel, sometimes you might need a small set of pliers to loosen the top knob. I will get the top loose and off first, tie a string to it, tie the other end to the bottom of the new cable to pull down from the bottom to feed the new cable through the loops.
Be sure and lube the new cable first before installing it. I use the cable lube sold at Canam/BRP dealers as it is designed for salt water application (seado- boats)as it is anticoanticorrosive XP-S is it's name. Some here have just used motor oil dripped down in the cable strung from a hook to hang it from and drip it in until it drips out the other end.