IM LOOKING TO INSTALL A TACH ON A HARLEY SPORTSTER 1980 3 WIRES BLACK GREEN AND YELLOW

If you have the above model Harley, you'll know it doesn't have a Tacho as standard, and that the factory-fitted risers prohibit installation on the handlebar centre. After selecting a suitable after-market indicator - there are plenty on J&P Cycle's website - you'll need to make or buy a simple, triangular bracket (polished stainless steel looks good), with a hole at each corner, picking up the two lower riser trim plate bolts. The third hole is for attaching the Tacho cannister and you'll probably need to drill a fourth hole to allow need cable routing - which will obviously require a rubber grommet. Or you can be clever and drill out the centre of your attachment bolt to achieve the same effect - don't forget to chamfer/smooth out the edges.
What is absolutely essential for the electrical connection of a tacho is a Crane Cams Tach Adaptor - p/n: 8-2050 - also available from J&P. On the 2004 XL883C, you'll need to follow the "Ground-Sensing" instructions, which are included with the adaptor. Remove seat & tank from the bike, run the Tacho wiring near the coil, disconnect coil plug at coil then cut that plug off (three wires), ensuring you have at least 3" of cable "Tail" going into the coil plug to attach additional wiring. Using a good-quality ratchet crimping tool and Red/Blue connectors, follow the connection table below:
a) Join Tacho Red wire (12v input to Tach), together with Tacho Blue wire (lighting), then add both to Blue wire from Tach Adaptor module. Join these (use a Blue sleeve crimp), to White/Black wire (12v supply from ignition switch), then rejoin White/Black wires.
b) Add long, Black wire from Tach module to Blue/Orange wire (one of the two 'Dual-Coil' switching lines from Ignition module to coil primary winding), then rejoin Blue/Orange wires as in a) above.
c) Add White wire from Tach module to Yellow/Blue wire (the other coil switching line), then rejoin Yellow/Blue as above.
d) Connect the Short, Black wire from tach module to Green wire from Tachometer (tape & tie back the short Grey wire to module).
e) Connect Black wire from Tacho to a good earth. I installed a large ring terminal with three "spare" earth wires under the head of a forward upper engine mounting bracket, but most of the Black wires on your Harley should be earth/ground wires - check first!
Now all you should have to do is wrap all your cable junctions with spiral wrapping or insulating tape, reconnect the coil plug, resecure any wiring looms/harnesses that you may have moved, refit tank & seat, then off you go - with shiny new tachometer telling you how fast your V-twin's turning.
Enjoy.