Replaced spark plugs. Car doesn't have a spark now?

I recently replaced the spark plugs in my 1968 Ford Galaxie 500. Before I did this, the car started right up. After I replaced them, I could not get the car to start. It wants to start, but I do not get a spark. After taking them out and replacing them, I got the car to start ONCE. Then again it won't start and I don't have a spark.
I disconnected the battery. I replaced each spark plug one at a time, I know each is in order.
It seems to me maybe I have a bad connection somewhere? Where should I look?

I take it that the starter spins the engine. If not, check the battery connections
If you did not change the spark plug wires, then the distributer should be good.
If the spark plugs were just a little too long, the pistons might have closed the gap on them.

Other than that, there may be other things that just happened to occur right now. If you are sure that it is lack of spark, just keep checking the electricity all the way back from the plug to the battery

Put the old spark plugs back in and try again - get it back to a running configuration - hard to tell what you could have done but that is one way to remove any changes you made. Check the ignition wire from the center of the distributor to the coil make sure it has been dislodged. Check point gap and make sure they aren't pitted or sticking.

The points or condenser could be faulty as this is NOT an electronic ignition; the ignition coil can be faulty

Start at the coil and see if there's about 9 volts or more present on the positive terminal of the coil with the key in the run and start positions. No voltage in run, but 9-10 volts in start indicates a bad ballast resistor or connection. 9-10 volts in run but no volts in start indicates a bad starter solenoid connection. Then test the negative side of the coil with a test light connected to the positive battery terminal while cranking the engine, it should flash. If it stays on the whole time, the points are not closing. If it stays off the whole time either the condenser is shorted or the points are not opening. If it flashes but there's still no spark from the coil, the coil or coil wire is bad.

Check each wire's resistance. It should be about 10K ohms per foot. Carelessly pulling on them can tear the wire. Don't forget the coil high tension. Then check the ignition points with a feeler gauge. If the gap it too small, adjust them, and check the timing. Check the coil and replace the condenser, just so you know it's good. If the timing is way off the timing chain may have jumped timing and I would not be surprised at that age but there still should be spark.

Plugs must connect to the engine block. They might have preservative on threads. Clean with acetone or similar. Make sure the block is connecting to the minus side of battery also.

1) Did you properly GAP the spark plugs? They typically do not come out of the box with the proper spark gap.

2) Have you replaced the distributor cap and rotor, or at least ensured that they are in good condition? Have you properly set the point gap?

3) Are you sure the ignition timing didn't get changed?

4) Are you sure that the ignition coil and ignition leads are tight and in good condition?

5) Are you sure there are no disconnected vacuum hoses?

6) Unless you can answer yes to all of the above, you have some work to do before we can discuss this further.

Obviously their is just a power lead knocked off or you have not connected, it can't be serious. Just go over what you took off and push wires or leads on correctly. No new plugs will stop it starting. Just retract the things you did, step by step.

Take of the rotor under the cap and see if it has a burnt spot under the 'spring' contact. It may be more visible looking down the inside. This happens quit a lot on the old type ignition system. The spark shorts through the rotor into the shaft looking for a ground. Just replace the rotor. And make sure the contact button in the center of the cap isn't worn off as well. Also check the coil wire with an ohm meter to make sure it isn't burned out from the bad rotor.

Weird. Since you have a vintage car, I'm sure you R careful. I doubt wires/coil./ distributor/points/rotor bad, as it DID run fine. I'm sure plug gap fine, too.

But, plugs sometimes bad out of box. Only takes 4 to make a no start, cold. Could also be wrong plugs. Put old ones in, like CB said. See if starts. If so, take the new ones back.