MSD 6a no start

I have a 92 mustang lx 5.0. I wanted to put an MSD on it. I got a used MSD 6a and an MSD harness and put them on. The car won't start.

I then sent the MSD 6a back to MSD and they checked it out saying there is nothing wrong with it.

I went back to the car and I had put an MSD coil on the car when I first got it. I took that coil off and I put the original coil back on. Still no start with the MSD hooked up.

In desperation I pulled the MSD 6AL off my 77 Volare race car, which runs just fine, and hooked it up to the stang. Still no start. Works fine on the Volare.

Here is the run down.
tried a MSD coil and the stock coil.
Tried a know good MSD box.
Tried all the testing listed on the MSD site. When hooked up there is no spark off the white wire.
I have triple checked the wires and tested all the continuity to all the wires. I have tested the MSD harness.
The engine is bone stock. (except for the MSD coil I put on.)
Works fine as long as the MSD is not in the middle.
I checked the voltages to all the wires and double checked ground.

I like the MSD unit. No I don't NEED it. But I want it . I do have an occasional miss at idle.

Anyone have any ideas. I call MSD but the tech I had didn't seem to knowledgeable.

Thanks,
Dan...