The glow plug inhibit switch has been eliminated. If you buy a new one it's just a jumper. So, you can jump it yourself. That'll either fix the problem or eliminate the glow plugs as the cause.
Next step, worn pump head...
The Constitution needs to be re-read, not re-written!
If you can't handle Dr. Seuss, how will you handle real life?
Current oil burners: MB GLK250 BlueTEC, John Deere X758
New ride: MB GLS450 - most stately
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510