The regulator/rectifier charges the battery by converting AC voltage from the stator into DC voltage for the battery. The byproduct of this conversion is the tach signal. Often times when a regulator/rectifier is faulty the tach not working will be the first clue. Now you need to see if the battery is changing, easy if you have a volt gauge, if not you need a voltage meter. Check your battery voltage with the engine off, let's say it reads 12.3V. Now start the engine and check again, it should read 13+ and rise with RPM to full power around 3000RPM. If the battery isn't charging and the tach doesn't work there's a really good chance the regulator/rectifier has failed. Take a look at it, it's a metal square about the size of a pack of non-filter cigarettes. It should have 2 yellow wires, a red wire, and a grey wire. Some of them are black and some are filled with an amber colored resin making the circuit board inside visible. You're looking for a brown or black spot inside the resin on the circuit board that would indicate something got hot and burned. If that's the case then it's bad, go ahead and replace it, it's a simple and straightforward repair that you can do yourself. Disconnect the batter before you start. The part typically costs about $125. The other possibility is that the charge coils on the stator have failed, but less likely as the regulator/rectifier is a much more common failure, cheaper part and easier replacement. Hope this helps.