I think that the ignition switch is bad on my 74 Charger. How do I tell. Turning the key does nothing, but I can start it by jumping it at the starter relay.

actually it is more likely the starter relay then then switch.

See if there is power coming in when you turn the key.
IF so the switch is fine.

Not sure what color it is on yours, but on mine it would be the yellow I think.

Per your request to check the switch function itself seperate the steering column electrical connector & jump 12V to the input wire in the col half of the connector & see if "out" circuit in the same col half of the connector (which goes to the solenoid terminal on the starter relay) has fire when you turn the key to "start". (www.mymopar.com has wiring diagrams to get the right color code) But first I would see if the yellow wire at the fender or firewall starter relay has fire when the key is turned to "start" & if not I'd seperate the black bulkhead connectors and clean the brass terminals (on both sides)& if no start pull apart the above steering col connector & check/clean its terminals. If the yellow wire does has fire in "start" see if the "grn" male terminal on the starter relay is grounded by grounding it (the male terminal) w a jumper wire & if it will now start adj the NSS at the trans (it should be grounded in P & N and very common for it to be out of adjustment). If the yellow "sol" wire has fire in "start" & the "grn" male terminal is grounded then the starter relay itself (though they rarely go bad) & check that it (the relay) is grounded well.

Try holding the key in the start position and move the shifter through the gears to see if it tries to start. If it does then your linkage is just out of adjustment. Also look at the neutral saftey switch plug on the rear drivers side of the trans to see that it's still plugged in.