1993 E300 4MATIC.I keep puting in new parts and my blower fan still will not run. I have put in a new dash controll unit, a new fan motor, check all the fuses and relays. I'm getting 12volts to the blower motor(red wire) when the inition is turned on, getting no reading on the blue wire at any time. I have check to power at the firewll plug, red at 12volts, gold at 3-6 volts depending on the setting on the fan speed setting. still no fan. I give-up. I'm tired of writting checks.

Have you checked the ground path, The fan gets power direct but the speed is controlled by the regulator in the ground side.

Does the ground come thru the controller or at the motor itself or is it thru the black post at the firewall plug?

Arthur Dalton would know this. Where is he?

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2012 E350
2006 Callaway SC560

Correct ,
The ground goes threw the regulator. Going from the connector on the fire wall to the regulator you have positive negative and control voltage.
The control voltage is what tells the regulator what speed to run by adjusting the ground.

Joe

Thanks, with everything new and working, I think I needed to replace the regulator below the fan unit from the very begining of my fan problems. Live and learn! I don't see whats left it could be.
Thanks