I have an 1984 Z28 that I just put a 350 in. The key starts the car but does not turn the engine off. Any ideas?

 

Bad ign switch.

 

Did you install an MSD ignition box at the same time?
It is common for the alternator to back feed through the ignition box and keep the engine running. The fix is to install a diode.

 

As always, see my signature.

Changing those parts didn't make the parts, or the design of the system, suddenly defective. That is not "the simplest explanation".

The simplest explanation is a workmanship issue.

Check for a short between the "motor" terminal of the solenoid (the one with the little copper strap going into the motor body) and the wire to the S terminal. Wire wrapped around something, loose strands, hooked up wrong, etc.

It's not impossible that the solenoid itself is bad, but it isn't as likely. Probably the second most likely: 95% chance it's wiring, 5% the solenoid, 0% anything else.

 

Did he mean continues to crank, or continues to run?

 

Right: sorry. That's what I get for doing this on a phone. Ignore me.

 

Found the problem, fan was back feeding into the system

 

Yes, that'll do that also. I assume you added a relay?

 

I did, thanks for your help.