a radom no spark, new TFI and Coil.

[trapez]

Throttle body 1985 GT Conv. Mustang.

Im in a situation where Im randomly getting no spark from the coil. This has been going on quit a while. I am now in position to test - the car is at home and not sparking. I just hope it doesnt start sparking before I find the problem.

last time I replaced both the TFI then the Coil. From my last test I pulled the wire from the coil and saw no spark but then later, minutes, it started sparking. At that point there was nothing to check, I replaced the coil then.

I know of one way to get it to start/spark, by disconecting the fuse type wire leading from the TFI. I have know idea what it is.
What is it? is it a clue? If I leave it disconected and drive a while I can then connect it back and all is ok


What is this? MSD?? It looks like I replaced it (passenger side below coil)



Any sugesstions on what to check first? Do I have an MSD type box??

thanks

[USMC302]

I would suggest tracing that white select box to see if it is connected to your ignition in any way, I didn't have that on my 85, but mine was not a convertable, so I'm unaware if it has something to do with the convertable top motor or not. If it is connected to the ignition, I would take it off and set the ignition coil back to stock connections.