Cheapest and best approach is to TEST before replacing parts. Corrosion is the enemy, so unplug, clean, replug all connectors between the rectifier and tach. To test the cable, just use a length of appropriate diameter wire long enoug to bypass, or, remove the tach and take it back to where a test lead can be used. Careful about loose wires and spinning flywheels.
Bridge rectifiers have a pair of diodes. Think of these as one way gates for electrons. The stator produces alternating current ( + then - ) So the rectifier allows the + pulses to flow to the battery and blocks the negative pulses. The tach measures these pulses, kind of an AC frequency meter, So the grey wire of the tach typically goes to one of the yellow wires from the stator, or the yellow with grey stripe. You can swap sides, and put the tach on the other pole of the rectifier. ( usually matters not which stator wire you take the tach pulse from. ) It it works on one side and not the other - one of the diodes may be shot. Test the rectifier anyway - cheap and easy to do.
A simple volt ohm meter or digital multi meter can test these. Harbor freight sells a cheap one for like $4 - $5 on sale. I keep on of those in the car. Much better ones are $25 - $60, and great ones are $200 - $500. (Fluke) A mid grade one can last many years, but you only need the basics. Add in a DVA and you can troubleshoot most outboard electrical issues that may arise.
In my experience most intermittent electrical problems are - bad connections ( corrosion and flexing failures of the wire. )- failing components due to heat - and cold solder joints.
Hope that helps.
Blaine
