Whenever I turn the climate control dial to max heat the aux water pump turns on and immediately shuts the blower/heater off. I have to turn off the ignition and turn back on for it to work again. If aux water pump is disconnected and wheel is set to max heat, there is no issue. I plugged in the connector to a 12v light source to see if maybe the aux pump was the problem, but it shut down again. I have traced the issue to be the white/brown wire on right hand connector of pin#7 of the push button unit. I have the factory service manual, but it does not show a relay or anything like that. Anyone have any ideas?

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1990 190E 3.0L