1) Connect battery and see 12 volts at the terminals, putting a voltmeter on the negative terminal and positive input at the wheelwell mounted solenoid I get 12.5 volts
2) Lights, radio, horn function
3) Turn key; starter whirs but doesn't actually turnover
4) All electrical then dies...I mean NOTHING. No horn, lights, radio, nothing. As if there is a completely dead battery.
5) Disconnect battery, wait somewhere between 15-30 minutes and reconnect battery, again have lights, horn, etc.
6) Turn key, everything dies again, NO POWER
Any thoughts on where to start?
Thanks!
A standing battery voltage of 12v is a bit on the low side. Should be a bit higher, but not your main problem at the moment.
Whirring but not turning over sounds like the starter bendix to me. Previous posts have mentioned checking out your battery/starter cables so I'll assume you checked them out.
If after the attempted start you have seemingly no power anywhere, you have corroded terminals/connections. Your fusible link will be good, but it's connectors may be corroded. Take apart and clean. Then take apart the bulkhead connectors and clean. They will most likely be crappy looking. Your column connector is less likely to be the problem but might as well take the two connectors apart and check their condition. When reassembling it would be beneficial to use a dielectric grease on them to help reduce future corrosion.
And as always with these cars, check your battery to rad support ground, and engine to firewall ground and make sure they are clean and tight.
Also as previously suggested, check the ammeter connections (with the battery disconnected)
Those steps should get rid of your 'disappearing' power