There are two power supplies (inputs) to the relay and 6 outputs (going to each glow plug). Both power inputs are 12-v but one is a small wire for small current and the other is a larger wire for more current. The small wire is used to "engage" the relay by closing the contract inside the relay. Once the contact is closed, this allows the main power from the large wire to power up the six outputs / glow plugs.

BIG INPUT WIRE:

I always have (high-amp / LARGER WIRE) 12-V supplied to the relay as I should. This 12-v is ALWAYS available regardless of ignition-key postion. This is GOOD.

SMALLER INPUT WIRE:

I do not always have (low-amp / SMALLER WIRE) 12-V supplied to the relay when I should have this voltage. This is bad. In other words, I should get 12-volts to close the relay anytime the key is turned from the "off" to the "on" postion. Perhaps one in 10 turns of the key result in no voltage thru this smaller wire. Therefore the relay does not close and the 12-V from the larger wire is not allowed to power up the glow plugs.

The relay operates as it should. I think the problem must be with the key / ignition switch or a computer problem. But this is a guess as I don't have a wiring diagram. I can't do anything about a computer problem so I will get a new or used ignition switch.

I don't think the strip fuse you mentioned is the problem because the relay operates as expected. I always have pleanty of amperage available anytime the relay is engaged. The problem is the signal to enage the relay is intermittant. This is not good.

As always, thanks for your input. Your input helps me to understand how the system works. It is always best to fully understand a system before you diagnose the system. I doubt I will be able to gather enough information to fully understand the system - but this ain't a perfert world.

__________________
Neil
1997 E300D - naturally aspirated
280,000 miles (as of November 2015)