When you say "it won't start" I assume you mean "the starter does not crank?"
Try actually troubleshooting it. Here's what I'd do. First, rig a test lamp with some long test leads so you can "get to stuff" and go to RadioSh** and buy a pack of clip leads Now this test lamp should NOT BE the kind you usually buy. rig one up with a STOP LAMP (turn signal) bulb. The reason you want a BIG bulb is so it will pull some current. This is important
Now EVERYTIME you start the car--until you find the problem, perform a test until you eliminate the problem. Open the hood before you insert the key, and if it won't crank, you can have a test rigged to see what you find
Because the car (evidently) runs OK, we can assume the ign switch is GETTING power. But there's a "long ways" OUT of the switch to the starter
Here's the basic path:
The switch itself could be bad in the start position
the connector on the switch could be loose/ corroded
the connection through the bulkhead connector could be loose/ corroded
From the bulkhead connector, the ign switch feeds one push on connector on the start relay
If this is an original '70 stick car, it had/ has a clutch safety switch.
So the relay should have FOUR terminals, just like a Torqueflite
So the second push on terminal of the start relay goes BACK through the firewall, to the clutch switch. (I don't remember---it may go through the bulkhead connector, or may be a separate wire through a grommet.
The above wire goes to the clutch safety switch.
The clutch safety switch, if still there, may be out of adjustment or defective
Last, the second terminal of the clutch safety switch goes to ground
AND the start relay could be bad (internal damage, rust, burned contacts)
OK, first thing to do is find out if you are getting power to the start relay FROM THE KEY
So, once again, instead of "jumping in" and twisting the key, "assume" that it won't crank and set up a test.
My (poor) diagram shows the ign sw. wire feeding the start relay is yellow. Pull this off, clip your test lamp on there to ground, and twist the key. If the light comes on, you MAY have power OK
If not, you have already isolated the problem from there---through the bulkhead--to the ign switch.
IF you DO get a light, hook the yellow back up, and pull loose the second push-on terminal.
Hook the lamp from the exposed terminal on the relay to ground, and twist the key. Get a light, then OK so far.
So is it the clutch switch?
Go inside the car, clip the test lamp on the un--grounded terminal of the safety switch, the other clip of the lamp to ground.
DO NOT push in the clutch. Twist the key, you should get a light. NOW push in the key, the light should go out, and the starter should crank.
You may have to repeat these a couple of times---if the trouble is not showing up.
Another thing to try is to dig around up by the column I ?? believe ?? that you can acess the ignition switch connector down at the column. If you can, probe the yellow (start) wire there with your lamp to ground when twisting the key.
These are simple circuits, guys. The biggest problem is figuring a way to connect your lamp, and to keep at it.
You can buy a lOT of parts and throw at the thing, then find out it was a simple wire end broke/ corroded, etc.