[Rick Parker]

We seem to go through MSD issues quite often and rarely is it actually the unit, so hang in there. To be certain the box is not at fault, start with the basics. IE:
Be sure the heavy red wire from the MSD box it attached to the battery side of the starter solenoid, and the small red wire is attached to a switched 12 volt source that is hot when the key is in the "ON/RUN" position AS WELL as the "START" position.
To actually test the box itself, set the parking brake, put trans mission in neutral, remove the coil wire from the top of the distributor and place it near the block or a good ground source, (not the carburetor). Disconnect the wire from the MSD box at the distributor. It has a 2 wire connector were it joins the distributor. While holding the long wire from the MSD box take a short piece (2"-4") of regular 16-18 gage wire forming a "U bend/jumper wire" in the small piece of wire and touch both conductors of the long wire at the same time. Each time you break the circuit as described a spark should be created at the coil/distributor wire near the ground souce. If you have spark each time then the MSD box is OK.

Rick