It seems that I have ruined two MSD 6AL boxes in a very short time as the first lasted one day the next one lasted 3 days.

I am using a Mopar Performance distributor,coil and ballast resistor.
This is all in a 70 Charger RT,4spd with 512RB engine.

After running the car I parked it and it would not start again. It would just crank over without firing. The first time it did that I tested the MSD 6AL box per MSD instructions and it showed that the box was burnt...we tried it on a friends car and confirmed it was toast....so I installed my MP orange ECU back on and it fired right up.

A couple of months later I purchase another MSD 6AL box and have it installed by a mechanic friend that I know. The same thing happened accept when I insalled my MP Orange ECU back on the car still would not start up...but would just crank over.

Did I fry the MP coil or do you think it did something to the MP distributor this time?

Most likely the MP coil,distributor and ballast are not compatible with the MSD 6AL box and that it was a bad idea. THe instructions came with a big list of non-compatible ignition stuff but none of the MP stuff was on there.

Just wondering what I probably fried in addition to the MSD 6AL box this time.

Why are you running a ballast resistor with a MSD? I'm successfully running a MP distributor with my MSD. Do you have a good ground and power feed to the MSD?

2 of my cars run MSD6s with the MP electronic dist & MSD coil, and one runs an old Accel coil (the big goofy old one). None run a ballast resistor, that circuit is bridged with a jumper wire. No need for a ballast. 2 have been bulletproof since the '80s, the 3rd is a new build. My MSDs are connected at the battery and I take care to have good grounds (at least 2). IIRC the MSD coil # is 5902.
Long ago I heard not to weld on a car with the MSD connected, and whether that's BS or not, I've always disconnected them if doing any welding, even exhaust work.

MSD 6, factory electronic dist and coil. No problems at all for ouver 10 years now.

Maybe there is a difference as mine is the MSD 6AL. Mine has the rev limiter but maybe something else is diffrent as well.