I have a 78 bronco with a pre 1974 460 it was running fine the the distibuter went I got one that is identical an now I have no spark an it won't try to start till I let off the key

 

What ignition system does it have on it? Dura Spark II? Points? Something else?

 

the distributer is from a 78 460 it original had points but was converted befor I got it

 

I even set the it 180 out an tried

 

OK, a 1978 460 distributor should be DuraSpark II. A DuraSpark II will have a distributor cap that is more "flat", that is, there is quite a bit of horizontal space between each spark plug wire tower on the cap, as compared to earlier caps where the plug towers are all close together.

The DuraSpark II ignition system fires the coil ONCE when power is removed (like when releasing the key from Start to Run). This one "fire" happens without triggering by the pickup coil in the distributor. This "fire when shutting off" is a nice troubleshooting aid. It checks out a lot of the ignition control module, the coil, the rotor, spark plug wire(s), etc.

When not getting spark when cranking, but getting one fire when turning the ignition off, the problem is usually a lack of pulse pickup from the distributor (or a break in wiring from distr. to ign. module).

If you have a DVM or ohmmeter and know how to use it:
Ignition Switch OFF, unplug connector at distributor, ID the Orange and Purple wires. Measure resistance into the distributor across the pins that connect to the Orange and Purple wires. Should see a couple/few hundred ohms. Should not be way low like 50 ohms, nor up in the couple thousands of ohms. This is checking continuity through the pickup coil. If the pickup coil is open (bad), the resistance will be sky high.

If it measures OK, plug it back in and unplug by the ignition control module, check resistance through the harness back towards the distributor on those two wires. Should read the same resistance. If it is open, then there is a break in the harness.

If it still reads OK, take the cap off of the distributor, and see if the reluctor wheel (looks like a funny 8-spoke paddlewheel) is there and not broken. The spokes should pass by the pole piece in the center of the pickup coil when the engine is cranked.

 

I have the exact symptoms that Torky2 describes except mine started when my original Control Box died and all I did was replace it and now it won't start until I let off the key and generally not until I try 4 or 5 times. I have not touched anything except changing the Control Box. I first tried one out of a junk yard and then a brand new one from Auto Zone. Same result. Before this it would start with about 1 1/2 turns every time. Oh this is a 390 in a '71 with the ignition from a '76 and it has been in there for at least 20 years and never a problem. What now?