You should be able to use all of the original dash lights as well as the turn and wiper stuff, I did when I used all Autometer gauges
On the new gauges you will have to get a donor harness to splice in if you don't want to butcher your existing wires.
I did a complete Autowire kit and used their supplied connectors along with plugins from Autometer.as you can see from the photos. I did not use an ampmeter but I have a voltmeter and an AFR gauge in a pilar pod.

I think I have most of the wiring sorted out, but what I'm still curious about is where to find a switched 12v supply. I want 12v with the key on, is the 5v transformer on he back of the cluster have a switched 12v. I will check mine when I get it apart but I am trying to use the car as long as possible before taking it apart. Thanks

The underdash harnesses are different for tach and standard cars.  It doesn't really matter though, because the way the factory tachs worked isn't going to make a modern tach work.  You will have to run a wire to the negative side of the coil to get a signal for a modern tach. 

Regarding keyed 12V, in a tach car there is a keyed 12V single female bullet connector that fed the tach and can be used (should be a red wire on the RH side of the cluster.  Another option is to just run a wire back from the + side of the coil when you run one for the tach sender.  This is what I did because I used a 14 gauge wire to prevent overloading the factory wiring.  IIRC the plug for the tach may not work during cranking either.  I used a molded two prong connector from NAPA at the firewall and drilled next to where the gauge feed comes through.  There should be a couple of factory dimples in that area where accessory wiring is meant to be run (AC, etc.).  With careful splicing techniques and careful routing only someone who knows classic Mustang wiring intimately could ever spot what I've done. 

Is that source hot in crank?  I definitely had an issue with no power going the the gauges during cranking while trying to use factory wiring.  I didn't want to lose gauge function during cranking because with electric gauges that tells me whether or not I have oil pressure during cranking, etc.allowing me to abort starting if its not building pressure.