on a '94 e320. I've checked: the 20A fuse, and each 30A fuse on the 2 relays; all are OK. Then I removed the dropping resistor behind the driver's headlight (strangest looking device) and an ohm meter across the terminals shows no resistance. Is this my problem?

regards,
Mark

Yes , but that will only effect the low fan operation.
High fan circuit by-passes this pre-resistor.
You can test both circuits individually.
The high fan should come on when you unplug the thermistor sensor on the thermo housing [ blue, two pole switch]
The low fan comes on when you jumper the pigtail wires from the high pressure sw at the reciever/drier.
These two test are to check the integrity of each fan speeds circuits.

Thanks Arthur,
For these tests is it necessary that the engine reach operating temperature, or is is sufficient to just power up by turning the ignition key to run position?
regards,
Mark

Key ON

Removed connection from the two pole blue switch at the thermostat, turned key to ON, and fans did not start. What shoul I do next?
mark

On the resistor , there is 1 wire on one end and 2 on the other ,,
Run a jumper from Bat + to the resistor terminal with the 2 wires on it.
This does not require key ON , as it is just a direct test to the fan motors.

Take a good look at that terminal too..