Re: 1958 mercury mark 58
A little editing on Scotts post if I may: Full "Wave" Bridge rectifier. Back in those days Selenium was the "known" semiconductor for rectifiers. They are easily recognized by their large fins, usually square, several of them spaced out from each other. Purpose was to change alternating current to direct current (flip over the neg half cycle of AC keeping it all on one side of zero volts). As years passed silicon became the semi-conductor of choice and you could get a FW bridge rectifier in a little packet. For high current applications it was usually housed in an alum tub with the rectifiers installed with hookup tabs extruding and filled with epoxy. These were bolted to a usually aluminum plate to get the heat out (heatsink) of the packet and into the ambient air. Thermal grease was used as required between the packet and the sink, depending upon the heat transfer needed and available assets for doing that.....ambient air temp, heat sink capability, and heat to dissipate from the rectifiers.
Nothing magic about a rectifier of either sort. You have 2 AC inputs from the stator and 2 outputs (a 4 terminal device): There is a positive lead that goes to the + battery terminal and a negative lead that goes to the - battery terminal. Sometimes there is indirect routing like via the starter solenoid input terminal for the + and the engine block for the -.
Concerns are to get diodes large enough for the charging current of your alternator and heat sinking to keep them cool. Back then a 9 amp alternator was probably tops so the 15 amp minimum Scott recommended sounds good to me. Radio Shack can supply the rectifier and if necessary the heat sink upon which you can mount the Silicon block.
HTH,
Mark
