I bought a book from Amazon about Yanmar diesel engines that covers all the diesels used on J30s among others. Its called Yanmar Inboards 1975-98 Diesels. Just search Amazon.com. They want $25 for it. Its worth every penny.
If your panel is at all similar to later J30s, you should be able to pull the panel out and pull the various bulbs to check their resistances. All you are looking for with the bulbs is continuity. If all the bulbs and other items requiring power on the panel are not functioning, it may be a lack of power to the panel itself. Turn the ignition switch on and check for 12 Volts on the power wire.
As for the tach sender, I'll send myself a reminder note to look up the resistance check value in my book. I'll post it back here soon along with anything else I might be able to find.
