I just looked at the diagram, and I was wrong. The control module switches positive, not ground. So forget what I said.

You need to check for 12V input at Pin 12 from Fuse #8. Then power goes out through Pins 3, 4, 6, 7, 8 and 11 to the resistor pack, where it gets stepped down or up to vary the blower speed, then to the blower. If the relay decides on low power, that would go out Pin 11, and full power is Pin 8. It looks like the input from the push-button unit is on Pins 2 and 9, and 10 is ground.

I need to think about how you would test this, since the problem could be in either the push-button unit (not sending a signal), or the fan relay (not sending power out).

You did check Fuses 7 and 8?

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe