Get a real hefty pushbutton switch, momentary contact, mount it on the left side of the dash so you can press it with left hand. Fuse it from the battery, and feed the output to glow plug harness hot side.

Problem solved for life:

Push and hold the button for ten seconds, just count in your head, in the tenth second release the button as you turn the key to "start".

To finish the job, remove glow plug relay and toss.

... never look back.

__________________
Cheers!
Scott McPhee

1987 300D