Date registered: Feb 2007
Vehicle: '74 & '78 450 SEL
Mentioned: 2 Post(s)
Quoted: 636 Post(s)
Ifyou've used three different switchgears and still have the stalling problem then it's likely not the switchgear that's faulty.
If there's black smoke from the exhaust I would check for plugs fouling from an overly rich condition after warm up.
If so, then start troubleshooting from there. (Leaking cold start valve, leaking injector(s), bad or misajusted air sensor, bad temp sensors etc...)