What could cause just the graphic-bar display on tachometer indicating boost pressure in intake manifold to quit working a 1985 nonturbo 300ZX sfter replacing alternator due overcharging?

There are a few things that could cause the graphic-bar display on the tachometer indicating boost pressure in the intake manifold to quit working after replacing the alternator in a 1985 non-turbo 300ZX:

- Improper wiring: Ensure that the alternator is correctly wired and connected to the tachometer. Check for any loose or disconnected wires.

- Fuse issue: Check the fuse for the tachometer and replace it if necessary.

- Faulty alternator: The new alternator may be defective or may not be compatible with the vehicle's electrical system. Try installing the original alternator to see if the problem persists.

- Malfunctioning tachometer: There may be an issue with the tachometer itself. This can be diagnosed by a professional mechanic or an automotive electrician.

Since the problem occurred after replacing the alternator, it's important to focus on the electrical connections and the compatibility of the new alternator with the vehicle's system. If you are unsure about any of these checks or repairs, it's best to consult a qualified mechanic for assistance.