Need help! Working on flooding issue on 96 chevrolet cab and chasis 7.4

I received truck after owner gave up at other shops. Stated that engine ram
fine as long as alternator was disconnected. Found that another shop had
installed a toggle switch in the single wire plug from alternator to ecm to
charge indicator,making it so the alternator could be switched off. I turned
switch off and engine idles great, takes throttle well, turn switch on and
right away begins to flood and barely idles but still takes throttle well. I
removed belt from alternator and left switch on and found that it runs great.
Seems as long as the alternator is not charging then everything is ok. Turn
switch off, disconnect either of the two alternator wires either plug or bat
connection or remove belt. As long as it is not charging, all is good. Have
had alternator checked and was over charging, they replaced regulator and
charges now at 14.6 but engine still wont run when charging. Odd though
that I can put a battery charger on truck while running with alternator
disconnected and it runns fine, even turned up to 18volts....help!!