350SDL, original owner, 147K miles. Original glow plug relay/module finally indicated trouble, replaced all glow plugs and relay/module. New relay/module failed.

Opened both relay/modules up and found the relay arm on the the number 3 cylinder burned off on both modules. If I remove the plug to the glow plug harness and apply 12VDC to the number 3 cylinder glow plug pin the number 3 glow plug gets warm and there is no indication of a short because the wire does not get hot-hot. Repeat the process on the other 5 cylinders and no indication of trouble.


Mechanic is stumped.

We need to find the problem before we fry another relay.

All ideas welcome.

Thank you.