Problems with MSD ignition - what could it be?!

[buba6]

OK, so now I am giving up. Need to ask for your ideas. I have a 302 supercharged Mercury Comet with a MSD ignition set. It includes:
- bilet distributor with dual pickup
- MSD 6 box
- MSD Boost Timing Master
- MSD blaster coil
- MSD spark plug wiers
All of those are connected as a separate wire installation, heavy red wires are connected directly to the battery, the small red wire is connected to battery with a switch in the middle, ground cables are directly to the battery.
Some times I get perfect spark, starting the car couple times in a row and no problem, than it seats for example for 30 minutes and doesn't want to spark any more. I have replaced the 6 box with a 7AL, the same result. Kicked out the BTM and fired only on MSD 6, the same. When I am shorting the wires comming from distributor, eliminating it, exactly the same, sometimes sparks, some times not.
Any idea what could it be? It is extremly hard to build a musclecar in europe, importing all the parts from USA and waiting for them weeks, and now this!
Please help!