Did you measure the power at the 12 volt terminal of the tach? There's usually a fuse between the fuse box and the tack (on the pink wire) that can blow. If you've got power, the service manual recommends a test at the distributor whereby you connect a light bulb to the tach terminal (ground one connector of the bulb). As the RPM's increase the bulb should grow dimmer. I really don't like the test and would rather connect a hand held tach to that terminal and see if it registers. If it does, disconnect the line from the distributor from the tach terminal and connect the handheld unit. If the handheld unit registers again, you've got a bad tach. If it doesn't, you've got a bad lead.
There's only two wires to contend with. I recommend buying a cluster off ebay to have for spares and testing. They aren't that expensive. Sometimes being able to hold something in your hand and look at it takes all the mystery out of it. See, if you had a spare cluster it would be an easy thing to connect the tach and see if it works.
I keep lots of spare things around....like headlight switches, gauge clusters, defogger timing relays, power window relays, ignition switches, wiper switches etc. Makes life a whole lot easier.
