No fire

[55312]

OK - I'm running out of ideas. I have a 427 top oiler that has run like a fire hose up until last week. Out of the blue, it won't start. At first I had it flooded and just assumed it was my impatience. After it sat and dried up a bit, it fired up and ran. I drove it down to hose it off and when I went to start it again, it wouldn't. Still convinced it was the fouled plugs, I put new ones in, got it fired up and took it out to hammer the cylinders clean for a short , spirited run. Parked it in the shop and when I went to take it out the next day....no go. I have an MSD 6AL box and MSD Billet distributor. Ran the MSD diagnostics by jumpering the mag pick up and it shoots nice blue fire out of the coil wire from the distributor so I assumed the MSD box and coil were OK. Ohmed out the mag pickup and it came in around 650 - 700 ohms. MSD says 400 to 900 is normal. The kicker is when I pull a plug and crank it over, I get no spark. I've spent all day tracing wires and did find the coil wired backwards with the positive and negative leads from the MSD box reversed and a black "mystery" wire doubled up on the negative pole. MSD said it would still run but don't double up wires on the coil posts. So.....I put the wires on the post where they belonged and took the "mystery" wire and added it to the block ground. Checked the box out again tonight and it passed the test with good blue spark from the coil wire but still no spark to the plugs. I'm stumped...........Anyone have any ideas? I hate swapping parts blind and would like to find a smoking gun. All I can think of is the Mag pickup in the distributor. I have a new cap and rotor coming tomorrow but doubt they are the problem. This engine has been stout and started fine a week ago!

All suggestions are welcome [u]