After working on the MPU, the rectifier board and the regulator board I installed the rectifier board and checked the voltages - all good. Then I installed the regulator / solenoid board and checked the voltages - all good. Then I installed the MPU and the fuse for the 12 volt blew. I removed the MPU and re-checked it on the bench - 6 flashes - good.
Today I replaced the 12 volt fuse and rechecked all the voltages - every thing checks good. Then I reinstalled the MPU but this time I only plugged in J4. Turned it on and I get seven flashes.
This looks like (to me) that I have a short somewhere outside the MPU that is causing the 12 volts fuse to blow. I only have one 4 amp fuse left - any ideas where too look?