Marine, don't replace working ignition parts just to get the tach running. The tach is not required to drive that car of yours.

As a lessons learnt for your books: I ALWAYS splice an inline fuse assembly into any hot wire going to the fusebox or the battery.

Most electric components (stereos, amps, tachs, aftermarket lights, etc) require it based on operating amperage requirements. It may be redundant protection in some cases but it is safer to err on that side.

In my humble (blown a few electric parts in the old days) opinion.