BC52,

Do you have some type of bypass circuit running through the 'R' terminal of the starter. It sure sounds like a START/RUN problem.

Although the HEI (GM) wants full voltage all the time, maybe your rig is wired to power the ignition through the solenoid relay during START and through the keyswitch during RUN.

If this were the case, it we more apt to be the contacts in the starter solenoid or wires than the keyswitch.

I don't know how your rig is wired and I'm vague when you say 'turn on the switch' then say 'turn on the key' so maybe I'm out in left field.

What you are describing is that the engine will only fire when the key flips back to the RUN position..is this right.

Stuart