Am in full agreement with Leatherman.... its gotta be one of millions of relays to be found on newer cars less than 20 yrs old.

Nobody will reply because post '83 electronic, engine management technology is sacred science beyond normal human comprehension..... and nobody sane would fiddle with existing electronic relay systems in their own backyard.

Is it glow plugs failing from wacky relay network- or just the dashboard light??

If it was me I'd soak the car at wash, causing this problem to occur.... then pull one glow plug and dangle it to see if it heats up.