Questions:

Does the operating lever work properly, or is it floppy? If so, sometimes the lever slips out of the switch, so it does nothing. A bit of superglue will fix that.

Otherwise, how many times have you used the cruise control switch for the turn signal? They only tolerate that so many times before the switch fails.....

Does it engage, the fade away, or surge a while then quit? If so, almost certainly the amplifier.

No action at all suddenly can be either actuator or amplifier, but you will be well served to have the current draw on the actuator tested betore installing a new amp -- if the actuator is bad, the current draw killed the amp, and a new amp will soon go the way of the old one.

The amplifier is probably behind the driver's side lower dash panel, held in by two screws with one large electrical connector. Typically, there is a chip in a socket beside the plug you will need to pull and swap into the replacement amp. Can't tell you how to get the panel off as I've never pulled one, though.

Peter

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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!