I have an original used under dash tach harness for sale the will need some repair. The two fittings that go to the tachometer have been cut off so you will need to find new ends and solder them on. There is another one or two ends that have also been cut off so they to will have to be replaced. Price is $425 for the harness. Email gandcmurphy@rogers.com if interested. Thanks.
That is referred to the dash cluster harness. The commonly referred to underdash harness is the more extensive harness that goes from the heater on passenger side of the dash all the way over to the headlights on the driver side and everything in between. The dash cluster harness plugs into the underdash harness. Best of luck on your sale.