So ever since I got the raw water pump back on and fired up old Perky and actually started going places in my own boat, I've been kinda bummed that none of the engine gauges showed any life.  No temp, no tach, no oil pressure, no nothing.  So I've puzzled over that for a couple weeks now and finally decided it was time to just sit down and figure out how to replace them.

Google brought me to a post on Cruisers' Forum in which the author said the first thing to know when replacing gauges is that there are three wires: one from the sender, and a positive and negative.  Wait a minute.  A positive and negative?  So those analog gauges need power?  So I immediately jumped up and ran over to the boat, fired up Perky, and started flipping switches on the panel, and wouldn't you know the panel has a switch labelled "Instruments" which totally does the trick?

So hopefully someday someone as puzzled as I will stumble on this and it will make their day.