W123 Aux Fan
 

Today I was ready to remove my aux fan after testing it - power up to the relay, no further. So after disconnecting the connector, I thought, "What the hell. While I'm down here, lets check power to the connector." Sure enough, there was power from the relay to the connector and after fiddling with it, I was able to listen to the roar of the aux fan. In the end, I cleaned up the connectors and left the fan where it sat - working.

So don't give up until you check up to the very end of the line.