Eric:

Yes, you could have toasted the traces so that you only have a connection through something else rather than directly to ground (this is called backfeed). Always take the negative battery cable loose when doing the instrument cluster so you don't short anything.

The only way to check is to remove it, so you are back to the oil line. You need a line wrench to get that fitting off, or at least a proper size metric -- adjustables will always round such fittings off.

Edge:

There is a vacuum switch on the back of the key switch for the shutoff, and yes, it can leak, either the switch or the rubber connectors or plastic lines. Test with a vac pump -- the line to the switch must hold vac in either key position, on or off.

The supply to the switch is brown, the line to the shutoff solenoid is brown with a blue stripe.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!