Read Your posting and want to offer a couple things.  It sounds like ammeter is wired backwards, just reverse wiring and will show charge.  60's came with a cut out relay which I have had some difficulites with aftermarket cut outs not &quot;releasing&quot; after shutting off tractor and essentially creating a drain on battery which shows on gauge.  Cleaning and adjusting contacts will sometimes fix problem.  Otherwise might look for delco cutouts which were OEM.  And lastly wiring the light switch can be tricky as well and sometimes wires get on wrong terminals.  Don't have any of my 60's close here to give you any advice on correct switch hookups though, sorry.  Hope this helps.