So I picked up a 1970 Duster today, got some newb questions

Make sure the fuse is good first but it's common for the dash bulbs and/or holders to go bad also. Then try rotating the headlight switch knob back and forth (in the "on" position) as previously mentioned. Worst case scenario is that you'll have to pull the instrument cluster and do some testing. It's not as bad as it sounds....only takes 15 minutes or so once you've done one. 2 hours if you haven't! Pull the battery cable first!
On the gauges, with the ignition OFF, pull the wire off the sender and hook up a jumper wire from the wire terminal to a good ground. Turn the ignition switch to the ON position. If you see the needle move on the gauge, immediately turn it back off. Don't let the gauge peg to the end or it might burn out. If the guage works with the jumper hooked up, the sender is bad. If the gauge still doesn't work, the wiring, gauge, or circuit board is probably the problem. Sometimes it's just a loose or corroded connection but you'll need to pull the cluster to tell. If neither fuel or temp work, it could be the dash voltage limiter also as previously mentioned. It plugs into the dash circuit board on your model. If you need to pull the fuel sender, drain the tank down to a 1/4 or less (by driving or siphon) and disconnect the hose and carefully remove the ground strap. It should connect the metal hose nipple on the sender to the steel line that heads up to the fuel pump by spanning over the hose area. Use a cold chisel or big screw driver and tap the lock ring to the left 1/4 turn or so until it falls off. If you've drained the tank down, you can then just pull the sender out. If you didn't drain the tank, you've just taken a gasoline shower and can't see to get to the garden hose to wash your eyes out! Remember, no smoking, open flame, or so much as a hot girl friend near that open tank! You may luck out and find that it's just the brass float that developed a hole and sank. To test the sender, connect 12 volts to the sender terminal with a jumper, then connect your 12 volt test light inline from the battery ground on one end to the frame of the sender on the other. Move the float lever up and down and see if the light dims and brightens. No? the sender is bad. Cuts in and out? the contact arm may be worn or bent to where it doesn't make a good contact anymore. Sometimes you can rebend it carefully and make it work again. Take care that you don't snag the fine wires of the potentiometer or you'll for sure have to get a new sender. You'll have to bend the tangs on the metal can that holds the potentiometer and covers the contact arm so it can be accessed but it's easy to do if you're carefull. Leave the electrical wire or strap connected and just move it aside so you can work. Sometimes the contact arm will break off and be laying loose in the can. It can be soldiered back on with no problem but attach it exactly where was before or your gauge won't be accurate.
Have fun!
Mark