As for the warning lights, look for a proper ground wire at the alternator. Look at the condition of the small red wire going to the field terminal on the alternator. This goes under the front pulley and is usually the first casualty of Biodegradable Wiring Harness disease.

Get that stuff straightened out and then worry about the tach. The tach should get it's signal from a white/red striped wire, normally hanging around loose in the dash. One of the other wires on your small tach will be a ground, the other for the light. If you can read terminal numbers or letters on the back of it, that will be helpful for diagnosis.
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Rob Bareiss, New London, CT 86 244, 87 244, 88 744