Glow plug light
 

Ok! Here is a glow plug activation and light issue, My1979 300TD has suddenly failed to activate the glow plugs and illuminate the glow plug light in the dash when the ignition switch is in the "glow pug" position but will activate light and glow plugs when the stater is cranking! The glow pug relay seems to be fine, It clicks loudly when the ignition is switched on and off plus the fact the pugs and light are activated again when the starter is engaged! While troubleshooting in the engine compartment I found a major vacuum leak in one of the rubber three way splitter. So can a low vacuum condition affect the ignition's activation of the glow plugs? Has any one experienced this issue and what was the solution?
Thanks for your help

Ok, solved the vacuum issue and it did not effect the ignition. The glow plugs are only activated as well as the panel light when the starter is engaged. A little back ground on the glow plugs. I upgraded to a parallel pencil glow plug system four years ago. The glow plugs have been working fine up until a few days ago.
I have checked all of the "GP" and they seem to check out. .05 ohms conductivity which is right inline with a new GP! Could this be the ignition switch screwing up?

One possibility of several perhaps. Perhaps the strongest one though. Not that common of an issue either to the best of my knowledge.