I have a 1978 E C with a 305.
I had been burning out capasitors in the distributor so I installed a MSD conversion kit. The kit included a cap, rotor, module, and high output coil. I also installed new wires so I could get the total benefit.
2 days ago I went to work and a couple of hours later tried to start it and it would not fire. I left until the end of the day and it started and ran normal. Yesterday the same thing happened. After a couple of hours it would not fire after all day, it started and it started and ran ok.
This morning it would not start. I finally could check and found that there is no spark. This should not happen with a new ignition.
Has anyone else had a problem like this??
elamott

Could be a Bad Ground connection in the ignition circuit. I'd look at the wires going to the cap/coil. When the car is not starting and / or getting fire use a DVM or a Simpson 260 check to see if your getting power to the cap through the pink/red +12v wire going into the cap.

If your not getting spark then it has to be before the distributor not in the distributor, assuming you hooked everything up correctly and I assume you did since it runs now and then. I'd guess when the truck is cold, cold maybe there is a brake in the wire that doesn't make good contact until it warms up some.

Also, look at the black ground wire and if your running an external tach, disconnect it when the ignition is not working to see if that fixes it. A bad tack could be grounding out the system or the wire going to the tack could be burnt somewhere and gets contact to the block shorting out the power.

My very best guess is all those caps (Condensers) you were replacing were not bad. With the right meter (A Simpson 260 VOM) you can check those caps to see if they are bad or not. I'm thinking that you have a wire that is internally broken or loose connection or grounding out.

When you can't get power to the cap, if that is what is happening you can use an external power source to make the connection. Disconnect the pink (Red) wire on the cap and go to a power lead someplace else and jump it to the cap, see if it works. It should.

Just some thoughts. Its difficult to actually say what is happening or wrong unless your actually there doing the diagnoses. :-(

Pete:
Thanks for the reply on my problem.
I do have power at the distributor. I have thought of the ground problem and tested it to the battery and came up with .4 ohms so that seemed ok. I did not consider the tach wire.
The last time it would not fire up was after I installed the MSD conversion and this is what I did.
I checked for power at the distributor that was ok. I then changed the coil, just to start eliminating things.
Still would not start. I then took out the MSD module and put in my old one. It fired up. I sent the MSD module back to the factory, they checked it out and said that it was ok. (That one blew me away because it would not start until I replaced the module.)
Regarding the tach. The tach wire plugs into the dist cap next to the red power wire. If that could ground the distributor out, it could be a possibility. Each time I replace the cap I move the wire???
One more thing, this problem started after I had the engine out, rebuilt and put it back in.
It is now running with my old module and coil with a new capasitor. It should last a couple of months,. (Based on the past)
Any other thoughts?????

Thanks again the info
Earl