well my rpm gauge doesnt work for me. my dad told me i need to replace the distributor cap. another person on the forums told me to check out the igniter out since all the gauges are powered by it. sounds like there might be something wrong with your igniter since all of them stopped working. dont forget to check the connections in the back of your gauge cluster to see if the wiring is ok, same goes for the igniter connections
heres the link to the thread i made. it might have some useful info in there and a diagram.
What is needed to get my RPM Gauge working??